PYTHON PROGRAMMING NOTES.pdf
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PYTHON PROGRAMMING III YEAR/II SEM MRCET PYTHON PROGRAMMING [R17A0554] LECTURE NOTES B.TECH III YEAR – II SEM (...
PYTHON PROGRAMMING III YEAR/II SEM MRCET PYTHON PROGRAMMING [R17A0554] LECTURE NOTES B.TECH III YEAR – II SEM (R17) (2019-20) DEPARTMENT OF COMPUTER SCIENCE AND ENGINEERING MALLA REDDY COLLEGE OF ENGINEERING & TECHNOLOGY (Autonomous Institution – UGC, Govt. of India) Recognized under 2(f) and 12 (B) of UGC ACT 1956 (Affiliated to JNTUH, Hyderabad, Approved by AICTE - Accredited by NBA & NAAC – ‘A’ Grade - ISO 9001:2015 Certified) Maisammaguda, Dhulapally (Post Via. Hakimpet), Secunderabad – 500100, Telangana State, India PYTHON PROGRAMMING III YEAR/II SEM MRCET SYLLABUS MALLA REDDY COLLEGE OF ENGINEERING AND TECHNOLOGY III Year B. Tech CSE -II SEM L T/P/D C 3 -/-/- 3 OPEN ELECTIVE III (R17A0554) PYTHON PROGRAMMING OBJECTIVES: To read and write simple Python programs. To develop Python programs with conditionals and loops. To define Python functions and call them. To use Python data structures –- lists, tuples, dictionaries. To do input/output with files in Python. UNIT I INTRODUCTION DATA, EXPRESSIONS, STATEMENTS Introduction to Python and installation, data types: Int, float, Boolean, string, and list; variables, expressions, statements, precedence of operators, comments; modules, functions--- function and its use, flow of execution, parameters and arguments. UNIT II CONTROL FLOW, LOOPS Conditionals: Boolean values and operators, conditional (if), alternative (if-else), chained conditional (if-elif-else); Iteration: while, for, break, continue. UNIT III FUNCTIONS, ARRAYS Fruitful functions: return values, parameters, local and global scope, function composition, recursion; Strings: string slices, immutability, string functions and methods, string module; Python arrays, Access the Elements of an Array, array methods. UNIT IV LISTS, TUPLES, DICTIONARIES Lists: list operations, list slices, list methods, list loop, mutability, aliasing, cloning lists, list parameters, list comprehension; Tuples: tuple assignment, tuple as return value, tuple comprehension; Dictionaries: operations and methods, comprehension; UNIT V FILES, EXCEPTIONS, MODULES, PACKAGES Files and exception: text files, reading and writing files, command line arguments, errors and exceptions, handling exceptions, modules (datetime, time, OS , calendar, math module), Explore packages. PYTHON PROGRAMMING III YEAR/II SEM MRCET OUTCOMES: Upon completion of the course, students will be able to Read, write, execute by hand simple Python programs. Structure simple Python programs for solving problems. Decompose a Python program into functions. Represent compound data using Python lists, tuples, dictionaries. Read and write data from/to files in Python Programs TEXT BOOKS 1.Allen B. Downey, ``Think Python: How to Think Like a Computer Scientist‘‘, 2nd edition, Updated for Python 3, Shroff/O‘Reilly Publishers, 2016. 2.R. Nageswara Rao, “Core Python Programming”, dreamtech 3. Python Programming: A Modern Approach, Vamsi Kurama, Pearson REFERENCE BOOKS: 1. Core Python Programming, W.Chun, Pearson. 2. Introduction to Python, Kenneth A. Lambert, Cengage 3. Learning Python, Mark Lutz, Orielly PYTHON PROGRAMMING III YEAR/II SEM MRCET INDEX UNIT TOPIC PAGE NO INTRODUCTION DATA, EXPRESSIONS, STATEMENTS 1 Introduction to Python and installation 1 data types: Int 6 float 7 Boolean 8 string 8 List 10 I variables 11 expressions 13 statements 16 precedence of operators 17 comments 18 modules 19 functions ---- function and its use 20 flow of execution 21 parameters and arguments 26 CONTROL FLOW, LOOPS 35 Conditionals: Boolean values and 35 operators, II conditional (if) 36 alternative (if-else) 37 chained conditional (if-elif-else) 39 Iteration: while, for, break, continue. 41 FUNCTIONS, ARRAYS 55 Fruitful functions: return values 55 parameters 57 local and global scope 59 function composition 62 III recursion 63 Strings: string slices 64 immutability 66 string functions and methods 67 string module 72 Python arrays 73 Access the Elements of an Array 75 Array methods 76 PYTHON PROGRAMMING III YEAR/II SEM MRCET LISTS, TUPLES, DICTIONARIES 78 Lists 78 list operations 79 list slices 80 list methods 81 list loop 83 mutability 85 aliasing 87 IV cloning lists 88 list parameters 89 list comprehension 90 Tuples 91 tuple assignment 94 tuple as return value 95 tuple comprehension 96 Dictionaries 97 operations and methods 97 comprehension 102 V FILES, EXCEPTIONS, 103 MODULES, PACKAGES Files and exception: text files 103 reading and writing files 104 command line arguments 109 errors and exceptions 112 handling exceptions 114 modules (datetime, time, OS , calendar, 121 math module) Explore packages 134 PYTHON PROGRAMMING III YEAR/II SEM MRCET UNIT – I INTRODUCTION DATA, EXPRESSIONS, STATEMENTS Introduction to Python and installation, data types: Int, float, Boolean, string, and list; variables, expressions, statements, precedence of operators, comments; modules, functions-- - function and its use, flow of execution, parameters and arguments. Introduction to Python and installation: Python is a widely used general-purpose, high level programming language. It was initially designed by Guido van Rossum in 1991 and developed by Python Software Foundation. It was mainly developed for emphasis on code readability, and its syntax allows programmers to express concepts in fewer lines of code. Python is a programming language that lets you work quickly and integrate systems more efficiently. There are two major Python versions- Python 2 and Python 3. On 16 October 2000, Python 2.0 was released with many new features. On 3rd December 2008, Python 3.0 was released with more testing and includes new features. Beginning with Python programming: 1) Finding an Interpreter: Before we start Python programming, we need to have an interpreter to interpret and run our programs. There are certain online interpreters like https://ide.geeksforgeeks.org/, http://ideone.com/ or http://codepad.org/ that can be used to start Python without installing an interpreter. Windows: There are many interpreters available freely to run Python scripts like IDLE (Integrated Development Environment) which is installed when you install the python software from http://python.org/downloads/ 2) Writing first program: # Script Begins Statement1 1 PYTHON PROGRAMMING III YEAR/II SEM MRCET Statement2 Statement3 # Script Ends Differences between scripting language and programming language: Why to use Python: The following are the primary factors to use python in day-to-day life: 1. Python is object-oriented Structure supports such concepts as polymorphism, operation overloading and multiple inheritance. 2. Indentation Indentation is one of the greatest feature in python 2 PYTHON PROGRAMMING III YEAR/II SEM MRCET 3. It’s free (open source) Downloading python and installing python is free and easy 4. It’s Powerful Dynamic typing Built-in types and tools Library utilities Third party utilities (e.g. Numeric, NumPy, sciPy) Automatic memory management 5. It’s Portable Python runs virtually every major platform used today As long as you have a compaitable python interpreter installed, python programs will run in exactly the same manner, irrespective of platform. 6. It’s easy to use and learn No intermediate compile Python Programs are compiled automatically to an intermediate form called byte code, which the interpreter then reads. This gives python the development speed of an interpreter without the performance loss inherent in purely interpreted languages. Structure and syntax are pretty intuitive and easy to grasp. 7. Interpreted Language Python is processed at runtime by python Interpreter 8. Interactive Programming Language Users can interact with the python interpreter directly for writing the programs 9. Straight forward syntax The formation of python syntax is simple and straight forward which also makes it popular. Installation: There are many interpreters available freely to run Python scripts like IDLE (Integrated Development Environment) which is installed when you install the python software from http://python.org/downloads/ Steps to be followed and remembered: Step 1: Select Version of Python to Install. Step 2: Download Python Executable Installer. Step 3: Run Executable Installer. Step 4: Verify Python Was Installed On Windows. 3 PYTHON PROGRAMMING III YEAR/II SEM MRCET Step 5: Verify Pip Was Installed. Step 6: Add Python Path to Environment Variables (Optional) Working with Python Python Code Execution: Python’s traditional runtime execution model: Source code you type is translated to byte code, which is then run by the Python Virtual Machine (PVM). Your code is automatically compiled, but then it is interpreted. Source Byte code Runtime PVM m.py m.pyc Source code extension is.py Byte code extension is.pyc (Compiled python code) There are two modes for using the Python interpreter: Interactive Mode Script Mode 4 PYTHON PROGRAMMING III YEAR/II SEM MRCET Running Python in interactive mode: Without passing python script file to the interpreter, directly execute code to Python prompt. Once you’re inside the python interpreter, then you can start. >>> print("hello world") hello world # Relevant output is displayed on subsequent lines without the >>> symbol >>> x=[0,1,2] # Quantities stored in memory are not displayed by default. >>> x #If a quantity is stored in memory, typing its name will display it. [0, 1, 2] >>> 2+3 5 The chevron at the beginning of the 1st line, i.e., the symbol >>> is a prompt the python interpreter uses to indicate that it is ready. If the programmer types 2+6, the interpreter replies 8. Running Python in script mode: 5 PYTHON PROGRAMMING III YEAR/II SEM MRCET Alternatively, programmers can store Python script source code in a file with the.py extension, and use the interpreter to execute the contents of the file. To execute the script by the interpreter, you have to tell the interpreter the name of the file. For example, if you have a script name MyFile.py and you're working on Unix, to run the script you have to type: python MyFile.py Working with the interactive mode is better when Python programmers deal with small pieces of code as you can type and execute them immediately, but when the code is more than 2-4 lines, using the script for coding can help to modify and use the code in future. Example: Data types: The data stored in memory can be of many types. For example, a student roll number is stored as a numeric value and his or her address is stored as alphanumeric characters. Python has various standard data types that are used to define the operations possible on them and the storage method for each of them. Int: Int, or integer, is a whole number, positive or negative, without decimals, of unlimited length. >>> print(24656354687654+2) 24656354687656 >>> print(20) 20 >>> print(0b10) 2 6 PYTHON PROGRAMMING III YEAR/II SEM MRCET >>> print(0B10) 2 >>> print(0X20) 32 >>> 20 20 >>> 0b10 2 >>> a=10 >>> print(a) 10 # To verify the type of any object in Python, use the type() function: >>> type(10) >>> a=11 >>> print(type(a)) Float: Float, or "floating point number" is a number, positive or negative, containing one or more decimals. Float can also be scientific numbers with an "e" to indicate the power of 10. >>> y=2.8 >>> y 2.8 >>> y=2.8 >>> print(type(y)) >>> type(.4) >>> 2. 7 PYTHON PROGRAMMING III YEAR/II SEM MRCET 2.0 Example: x = 35e3 y = 12E4 z = -87.7e100 print(type(x)) print(type(y)) print(type(z)) Output: Boolean: Objects of Boolean type may have one of two values, True or False: >>> type(True) >>> type(False) String: 1. Strings in Python are identified as a contiguous set of characters represented in the quotation marks. Python allows for either pairs of single or double quotes. 'hello' is the same as "hello". Strings can be output to screen using the print function. For example: print("hello"). >>> print("mrcet college") mrcet college >>> type("mrcet college") 8 PYTHON PROGRAMMING III YEAR/II SEM MRCET >>> print('mrcet college') mrcet college >>> " " '' If you want to include either type of quote character within the string, the simplest way is to delimit the string with the other type. If a string is to contain a single quote, delimit it with double quotes and vice versa: >>> print("mrcet is an autonomous (') college") mrcet is an autonomous (') college >>> print('mrcet is an autonomous (") college') mrcet is an autonomous (") college Suppressing Special Character: Specifying a backslash (\) in front of the quote character in a string “escapes” it and causes Python to suppress its usual special meaning. It is then interpreted simply as a literal single quote character: >>> print("mrcet is an autonomous (\') college") mrcet is an autonomous (') college >>> print('mrcet is an autonomous (\") college') mrcet is an autonomous (") college The following is a table of escape sequences which cause Python to suppress the usual special interpretation of a character in a string: >>> print('a\....b') a....b >>> print('a\ b\ c') 9 PYTHON PROGRAMMING III YEAR/II SEM MRCET abc >>> print('a \n b') a b >>> print("mrcet \n college") mrcet college Escape Usual Interpretation of Sequence Character(s) After Backslash “Escaped” Interpretation \' Terminates string with single quote opening delimiter Literal single quote (') character \" Terminates string with double quote opening delimiter Literal double quote (") character \newline Terminates input line Newline is ignored \\ Introduces escape sequence Literal backslash (\) character In Python (and almost all other common computer languages), a tab character can be specified by the escape sequence \t: >>> print("a\tb") a b List: It is a general purpose most widely used in data structures List is a collection which is ordered and changeable and allows duplicate members. (Grow and shrink as needed, sequence type, sortable). To use a list, you must declare it first. Do this using square brackets and separate values with commas. We can construct / create list in many ways. Ex: >>> list1=[1,2,3,'A','B',7,8,[10,11]] >>> print(list1) [1, 2, 3, 'A', 'B', 7, 8, [10, 11]] 10 PYTHON PROGRAMMING III YEAR/II SEM MRCET ---------------------- >>> x=list() >>> x [] -------------------------- >>> tuple1=(1,2,3,4) >>> x=list(tuple1) >>> x [1, 2, 3, 4] Variables: Variables are nothing but reserved memory locations to store values. This means that when you create a variable you reserve some space in memory. Based on the data type of a variable, the interpreter allocates memory and decides what can be stored in the reserved memory. Therefore, by assigning different data types to variables, you can store integers, decimals or characters in these variables. Rules for Python variables: A variable name must start with a letter or the underscore character A variable name cannot start with a number A variable name can only contain alpha-numeric characters and underscores (A-z, 0-9, and _ ) Variable names are case-sensitive (age, Age and AGE are three different variables) Assigning Values to Variables: Python variables do not need explicit declaration to reserve memory space. The declaration happens automatically when you assign a value to a variable. The equal sign (=) is used to assign values to variables. The operand to the left of the = operator is the name of the variable and the operand to the right of the = operator is the value stored in the variable. 11 PYTHON PROGRAMMING III YEAR/II SEM MRCET For example − a= 100 # An integer assignment b = 1000.0 # A floating point c = "John" # A string print (a) print (b) print (c) This produces the following result − 100 1000.0 John Multiple Assignment: Python allows you to assign a single value to several variables simultaneously. For example : a=b=c=1 Here, an integer object is created with the value 1, and all three variables are assigned to the same memory location. You can also assign multiple objects to multiple variables. For example − a,b,c = 1,2,"mrcet“ Here, two integer objects with values 1 and 2 are assigned to variables a and b respectively, and one string object with the value "john" is assigned to the variable c. Output Variables: The Python print statement is often used to output variables. Variables do not need to be declared with any particular type and can even change type after they have been set. 12 PYTHON PROGRAMMING III YEAR/II SEM MRCET x=5 # x is of type int x = "mrcet " # x is now of type str print(x) Output: mrcet To combine both text and a variable, Python uses the “+” character: Example x = "awesome" print("Python is " + x) Output Python is awesome You can also use the + character to add a variable to another variable: Example x = "Python is " y = "awesome" z=x+y print(z) Output: Python is awesome Expressions: An expression is a combination of values, variables, and operators. An expression is evaluated using assignment operator. Examples: Y=x + 17 >>> x=10 >>> z=x+20 >>> z 30 13 PYTHON PROGRAMMING III YEAR/II SEM MRCET >>> x=10 >>> y=20 >>> c=x+y >>> c 30 A value all by itself is a simple expression, and so is a variable. >>> y=20 >>> y 20 Python also defines expressions only contain identifiers, literals, and operators. So, Identifiers: Any name that is used to define a class, function, variable module, or object is an identifier. Literals: These are language-independent terms in Python and should exist independently in any programming language. In Python, there are the string literals, byte literals, integer literals, floating point literals, and imaginary literals. Operators: In Python you can implement the following operations using the corresponding tokens. 14 PYTHON PROGRAMMING III YEAR/II SEM MRCET Operator Token add + subtract - multiply * Integer Division / remainder % Binary left shift > and & or \ Less than < Greater than > Less than or equal to = Check equality == Check not equal != 15 PYTHON PROGRAMMING III YEAR/II SEM MRCET Some of the python expressions are: Generator expression: Syntax: ( compute(var) for var in iterable ) >>> x = (i for i in 'abc') #tuple comprehension >>> x >>> print(x) You might expect this to print as ('a', 'b', 'c') but it prints as The result of a tuple comprehension is not a tuple: it is actually a generator. The only thing that you need to know now about a generator now is that you can iterate over it, but ONLY ONCE. Conditional expression: Syntax: true_value if Condition else false_value >>> x = "1" if True else "2" >>> x '1' Statements: A statement is an instruction that the Python interpreter can execute. We have normally two basic statements, the assignment statement and the print statement. Some other kinds of statements that are if statements, while statements, and for statements generally called as control flows. Examples: An assignment statement creates new variables and gives them values: >>> x=10 16 PYTHON PROGRAMMING III YEAR/II SEM MRCET >>> college="mrcet" An print statement is something which is an input from the user, to be printed / displayed on to the screen (or ) monitor. >>> print("mrcet colege") mrcet college Precedence of Operators: Operator precedence affects how an expression is evaluated. For example, x = 7 + 3 * 2; here, x is assigned 13, not 20 because operator * has higher precedence than +, so it first multiplies 3*2 and then adds into 7. Example 1: >>> 3+4*2 11 Multiplication gets evaluated before the addition operation >>> (10+10)*2 40 Parentheses () overriding the precedence of the arithmetic operators Example 2: a = 20 b = 10 c = 15 d=5 e=0 e = (a + b) * c / d #( 30 * 15 ) / 5 print("Value of (a + b) * c / d is ", e) e = ((a + b) * c) / d # (30 * 15 ) / 5 print("Value of ((a + b) * c) / d is ", e) e = (a + b) * (c / d); # (30) * (15/5) 17 PYTHON PROGRAMMING III YEAR/II SEM MRCET print("Value of (a + b) * (c / d) is ", e) e = a + (b * c) / d; # 20 + (150/5) print("Value of a + (b * c) / d is ", e) Output: C:/Users/MRCET/AppData/Local/Programs/Python/Python38-32/pyyy/opprec.py Value of (a + b) * c / d is 90.0 Value of ((a + b) * c) / d is 90.0 Value of (a + b) * (c / d) is 90.0 Value of a + (b * c) / d is 50.0 Comments: Single-line comments begins with a hash(#) symbol and is useful in mentioning that the whole line should be considered as a comment until the end of line. A Multi line comment is useful when we need to comment on many lines. In python, triple double quote(“ “ “) and single quote(‘ ‘ ‘)are used for multi-line commenting. Example: Output: C:/Users/MRCET/AppData/Local/Programs/Python/Python38-32/pyyy/comm.py 30 18 PYTHON PROGRAMMING III YEAR/II SEM MRCET Modules: Modules: Python module can be defined as a python program file which contains a python code including python functions, class, or variables. In other words, we can say that our python code file saved with the extension (.py) is treated as the module. We may have a runnable code inside the python module. A module in Python provides us the flexibility to organize the code in a logical way. To use the functionality of one module into another, we must have to import the specific module. Syntax: import Every module has its own functions, those can be accessed with. (dot) Note: In python we have help () Enter the name of any module, keyword, or topic to get help on writing Python programs and using Python modules. To quit this help utility and return to the interpreter, just type "quit". Some of the modules like os, date, and calendar so on…… >>> import sys >>> print(sys.version) 3.8.0 (tags/v3.8.0:fa919fd, Oct 14 2019, 19:21:23) [MSC v.1916 32 bit (Intel)] >>> print(sys.version_info) sys.version_info(major=3, minor=8, micro=0, releaselevel='final', serial=0) >>> print(calendar.month(2021,5)) >>> print(calendar.isleap(2020)) True >>> print(calendar.isleap(2017)) False 19 PYTHON PROGRAMMING III YEAR/II SEM MRCET Functions: Functions and its use: Function is a group of related statements that perform a specific task. Functions help break our program into smaller and modular chunks. As our program grows larger and larger, functions make it more organized and manageable. It avoids repetition and makes code reusable. Basically, we can divide functions into the following two types: 1. Built-in functions - Functions that are built into Python. Ex: abs(),all().ascii(),bool()………so on…. integer = -20 print('Absolute value of -20 is:', abs(integer)) Output: Absolute value of -20 is: 20 2. User-defined functions - Functions defined by the users themselves. def add_numbers(x,y): sum = x + y return sum print("The sum is", add_numbers(5, 20)) Output: The sum is 25 Flow of Execution: 1. The order in which statements are executed is called the flow of execution 2. Execution always begins at the first statement of the program. 3. Statements are executed one at a time, in order, from top to bottom. 4. Function definitions do not alter the flow of execution of the program, but remember that statements inside the function are not executed until the function is called. 5. Function calls are like a bypass in the flow of execution. Instead of going to the next statement, the flow jumps to the first line of the called function, executes all the statements there, and then comes back to pick up where it left off. 20 PYTHON PROGRAMMING III YEAR/II SEM MRCET Note: When you read a program, don’t read from top to bottom. Instead, follow the flow of execution. This means that you will read the def statements as you are scanning from top to bottom, but you should skip the statements of the function definition until you reach a point where that function is called. Example: #example for flow of execution print("welcome") for x in range(3): print(x) print("Good morning college") Output: C:/Users/MRCET/AppData/Local/Programs/Python/Python38-32/pyyy/flowof.py welcome 0 1 2 Good morning college The flow/order of execution is: 2,3,4,3,4,3,4,5 ------------------------------------------ 21 PYTHON PROGRAMMING III YEAR/II SEM MRCET Output: C:/Users/MRCET/AppData/Local/Programs/Python/Python38-32/pyyy/flowof.py hi hello Good morning mrcet done! The flow/order of execution is: 2,5,6,7,2,3,4,7,8 Parameters and arguments: Parameters are passed during the definition of function while Arguments are passed during the function call. Example: #here a and b are parameters def add(a,b): #//function definition return a+b #12 and 13 are arguments #function call result=add(12,13) print(result) Output: C:/Users/MRCET/AppData/Local/Programs/Python/Python38-32/pyyy/paraarg.py 25 There are three types of Python function arguments using which we can call a function. 1. Default Arguments 2. Keyword Arguments 3. Variable-length Arguments Syntax: def functionname(): 22 PYTHON PROGRAMMING III YEAR/II SEM MRCET statements... functionname() Function definition consists of following components: 1. Keyword def indicates the start of function header. 2. A function name to uniquely identify it. Function naming follows the same rules of writing identifiers in Python. 3. Parameters (arguments) through which we pass values to a function. They are optional. 4. A colon (:) to mark the end of function header. 5. Optional documentation string (docstring) to describe what the function does. 6. One or more valid python statements that make up the function body. Statements must have same indentation level (usually 4 spaces). 7. An optional return statement to return a value from the function. Example: def hf(): hello world hf() In the above example we are just trying to execute the program by calling the function. So it will not display any error and no output on to the screen but gets executed. To get the statements of function need to be use print(). #calling function in python: def hf(): print("hello world") hf() Output: hello world ------------------------------- 23 PYTHON PROGRAMMING III YEAR/II SEM MRCET def hf(): print("hw") print("gh kfjg 66666") hf() hf() hf() Output: hw gh kfjg 66666 hw gh kfjg 66666 hw gh kfjg 66666 --------------------------------- def add(x,y): c=x+y print(c) add(5,4) Output: 9 def add(x,y): c=x+y return c print(add(5,4)) Output: 9 ----------------------------------- 24 PYTHON PROGRAMMING III YEAR/II SEM MRCET def add_sub(x,y): c=x+y d=x-y return c,d print(add_sub(10,5)) Output: (15, 5) The return statement is used to exit a function and go back to the place from where it was called. This statement can contain expression which gets evaluated and the value is returned. If there is no expression in the statement or the return statement itself is not present inside a function, then the function will return the None object. def hf(): return "hw" print(hf()) Output: hw ---------------------------- def hf(): return "hw" hf() Output: C:/Users/MRCET/AppData/Local/Programs/Python/Python38-32/pyyy/fu.py >>> 25 PYTHON PROGRAMMING III YEAR/II SEM MRCET ------------------------------------- def hello_f(): return "hellocollege" print(hello_f().upper()) Output: HELLOCOLLEGE # Passing Arguments def hello(wish): return '{}'.format(wish) print(hello("mrcet")) Output: mrcet ------------------------------------------------ Here, the function wish() has two parameters. Since, we have called this function with two arguments, it runs smoothly and we do not get any error. If we call it with different number of arguments, the interpreter will give errors. def wish(name,msg): """This function greets to the person with the provided message""" print("Hello",name + ' ' + msg) wish("MRCET","Good morning!") Output: Hello MRCET Good morning! 26 PYTHON PROGRAMMING III YEAR/II SEM MRCET Below is a call to this function with one and no arguments along with their respective error messages. >>> wish("MRCET") # only one argument TypeError: wish() missing 1 required positional argument: 'msg' >>> wish() # no arguments TypeError: wish() missing 2 required positional arguments: 'name' and 'msg' ---------------------------------------------- def hello(wish,hello): return “hi” '{},{}'.format(wish,hello) print(hello("mrcet","college")) Output: himrcet,college #Keyword Arguments When we call a function with some values, these values get assigned to the arguments according to their position. Python allows functions to be called using keyword arguments. When we call functions in this way, the order (position) of the arguments can be changed. (Or) If you have some functions with many parameters and you want to specify only some of them, then you can give values for such parameters by naming them - this is called keyword arguments - we use the name (keyword) instead of the position (which we have been using all along) to specify the arguments to the function. There are two advantages - one, using the function is easier since we do not need to worry about the order of the arguments. Two, we can give values to only those parameters which we want, provided that the other parameters have default argument values. def func(a, b=5, c=10): print 'a is', a, 'and b is', b, 'and c is', c 27 PYTHON PROGRAMMING III YEAR/II SEM MRCET func(3, 7) func(25, c=24) func(c=50, a=100) Output: a is 3 and b is 7 and c is 10 a is 25 and b is 5 and c is 24 a is 100 and b is 5 and c is 50 Note: The function named func has one parameter without default argument values, followed by two parameters with default argument values. In the first usage, func(3, 7), the parameter a gets the value 3, the parameter b gets the value 5 and c gets the default value of 10. In the second usage func(25, c=24), the variable a gets the value of 25 due to the position of the argument. Then, the parameter c gets the value of 24 due to naming i.e. keyword arguments. The variable b gets the default value of 5. In the third usage func(c=50, a=100), we use keyword arguments completely to specify the values. Notice, that we are specifying value for parameter c before that for a even though a is defined before c in the function definition. For example: if you define the function like below def func(b=5, c=10,a): # shows error : non-default argument follows default argument ------------------------------------------------------- def print_name(name1, name2): """ This function prints the name """ print (name1 + " and " + name2 + " are friends") #calling the function print_name(name2 = 'A',name1 = 'B') 28 PYTHON PROGRAMMING III YEAR/II SEM MRCET Output: B and A are friends #Default Arguments Function arguments can have default values in Python. We can provide a default value to an argument by using the assignment operator (=) def hello(wish,name='you'): return '{},{}'.format(wish,name) print(hello("good morning")) Output: good morning,you --------------------------------------------- def hello(wish,name='you'): return '{},{}'.format(wish,name) //print(wish + ‘ ‘ + name) print(hello("good morning","nirosha")) // hello("good morning","nirosha") Output: good morning,nirosha // good morning nirosha Note: Any number of arguments in a function can have a default value. But once we have a default argument, all the arguments to its right must also have default values. This means to say, non-default arguments cannot follow default arguments. For example, if we had defined the function header above as: def hello(name='you', wish): Syntax Error: non-default argument follows default argument ------------------------------------------ def sum(a=4, b=2): #2 is supplied as default argument 29 PYTHON PROGRAMMING III YEAR/II SEM MRCET """ This function will print sum of two numbers if the arguments are not supplied it will add the default value """ print (a+b) sum(1,2) #calling with arguments sum( ) #calling without arguments Output: 3 6 Variable-length arguments Sometimes you may need more arguments to process function then you mentioned in the definition. If we don’t know in advance about the arguments needed in function, we can use variable-length arguments also called arbitrary arguments. For this an asterisk (*) is placed before a parameter in function definition which can hold non-keyworded variable-length arguments and a double asterisk (**) is placed before a parameter in function which can hold keyworded variable-length arguments. If we use one asterisk (*) like *var, then all the positional arguments from that point till the end are collected as a tuple called ‘var’ and if we use two asterisks (**) before a variable like **var, then all the positional arguments from that point till the end are collected as a dictionary called ‘var’. def wish(*names): """This function greets all the person in the names tuple.""" # names is a tuple with arguments for name in names: print("Hello",name) wish("MRCET","CSE","SIR","MADAM") 30 PYTHON PROGRAMMING III YEAR/II SEM MRCET Output: Hello MRCET Hello CSE Hello SIR Hello MADAM #Program to find area of a circle using function use single return value function with argument. pi=3.14 def areaOfCircle(r): return pi*r*r r=int(input("Enter radius of circle")) print(areaOfCircle(r)) Output: C:/Users/MRCET/AppData/Local/Programs/Python/Python38-32/pyyy/fu1.py Enter radius of circle 3 28.259999999999998 #Program to write sum different product and using arguments with return value function. def calculete(a,b): total=a+b diff=a-b prod=a*b div=a/b mod=a%b 31 PYTHON PROGRAMMING III YEAR/II SEM MRCET return total,diff,prod,div,mod a=int(input("Enter a value")) b=int(input("Enter b value")) #function call s,d,p,q,m = calculete(a,b) print("Sum= ",s,"diff= ",d,"mul= ",p,"div= ",q,"mod= ",m) #print("diff= ",d) #print("mul= ",p) #print("div= ",q) #print("mod= ",m) Output: C:/Users/MRCET/AppData/Local/Programs/Python/Python38-32/pyyy/fu1.py Enter a value 5 Enter b value 6 Sum= 11 diff= -1 mul= 30 div= 0.8333333333333334 mod= 5 #program to find biggest of two numbers using functions. def biggest(a,b): if a>b : return a else : return b a=int(input("Enter a value")) b=int(input("Enter b value")) #function call big= biggest(a,b) print("big number= ",big) Output: 32 PYTHON PROGRAMMING III YEAR/II SEM MRCET C:/Users/MRCET/AppData/Local/Programs/Python/Python38-32/pyyy/fu1.py Enter a value 5 Enter b value-2 big number= 5 #program to find biggest of two numbers using functions. (nested if) def biggest(a,b,c): if a>b : if a>c : return a else : return c else : if b>c : return b else : return c a=int(input("Enter a value")) b=int(input("Enter b value")) c=int(input("Enter c value")) #function call big= biggest(a,b,c) print("big number= ",big) Output: C:/Users/MRCET/AppData/Local/Programs/Python/Python38-32/pyyy/fu1.py Enter a value 5 Enter b value -6 Enter c value 7 big number= 7 #Writer a program to read one subject mark and print pass or fail use single return values function with argument. def result(a): if a>40: return "pass" 33 PYTHON PROGRAMMING III YEAR/II SEM MRCET else: return "fail" a=int(input("Enter one subject marks")) print(result(a)) Output: C:/Users/MRCET/AppData/Local/Programs/Python/Python38-32/pyyy/fu1.py Enter one subject marks 35 fail #Write a program to display mrecet cse dept 10 times on the screen. (while loop) def usingFunctions(): count =0 while count>> 5 == 5 True >>> 5 == 6 False True and False are special values that belong to the type bool; they are not strings: >>> type(True) >>> type(False) The == operator is one of the relational operators; the others are: x != y # x is not equal to y x > y # x is greater than y x < y # x is less than y x >= y # x is greater than or equal to y x 2: print(a, "is greater") print("done") a = -1 if a < 0: print(a, "a is smaller") print("Finish") Output: 36 PYTHON PROGRAMMING III YEAR/II SEM MRCET C:/Users/MRCET/AppData/Local/Programs/Python/Python38-32/pyyy/if1.py 3 is greater done -1 a is smaller Finish -------------------------------- a=10 if a>9: print("A is Greater than 9") Output: C:/Users/MRCET/AppData/Local/Programs/Python/Python38-32/pyyy/if2.py A is Greater than 9 Alternative if (If-Else): An else statement can be combined with an if statement. An else statement contains the block of code (false block) that executes if the conditional expression in the if statement resolves to 0 or a FALSE value. The else statement is an optional statement and there could be at most only one else Statement following if. Syntax of if - else : if test expression: Body of if stmts else: Body of else stmts If - else Flowchart : 37 PYTHON PROGRAMMING III YEAR/II SEM MRCET Fig: Operation of if – else statement Example of if - else: a=int(input('enter the number')) if a>5: print("a is greater") else: print("a is smaller than the input given") Output: C:/Users/MRCET/AppData/Local/Programs/Python/Python38-32/pyyy/ifelse.py enter the number 2 a is smaller than the input given ---------------------------------------- a=10 b=20 if a>b: print("A is Greater than B") else: print("B is Greater than A") Output: C:/Users/MRCET/AppData/Local/Programs/Python/Python38-32/pyyy/if2.py B is Greater than A 38 PYTHON PROGRAMMING III YEAR/II SEM MRCET Chained Conditional: (If-elif-else): The elif statement allows us to check multiple expressions for TRUE and execute a block of code as soon as one of the conditions evaluates to TRUE. Similar to the else, the elif statement is optional. However, unlike else, for which there can be at most one statement, there can be an arbitrary number of elif statements following an if. Syntax of if – elif - else : If test expression: Body of if stmts elif test expression: Body of elif stmts else: Body of else stmts Flowchart of if – elif - else: Fig: Operation of if – elif - else statement Example of if - elif – else: a=int(input('enter the number')) b=int(input('enter the number')) c=int(input('enter the number')) if a>b: 39 PYTHON PROGRAMMING III YEAR/II SEM MRCET print("a is greater") elif b>c: print("b is greater") else: print("c is greater") Output: C:/Users/MRCET/AppData/Local/Programs/Python/Python38-32/pyyy/ifelse.py enter the number5 enter the number2 enter the number9 a is greater >>> C:/Users/MRCET/AppData/Local/Programs/Python/Python38-32/pyyy/ifelse.py enter the number2 enter the number5 enter the number9 c is greater ----------------------------- var = 100 if var == 200: print("1 - Got a true expression value") print(var) elif var == 150: print("2 - Got a true expression value") print(var) elif var == 100: print("3 - Got a true expression value") print(var) else: print("4 - Got a false expression value") print(var) print("Good bye!") Output: C:/Users/MRCET/AppData/Local/Programs/Python/Python38-32/pyyy/ifelif.py 3 - Got a true expression value 100 Good bye! 40 PYTHON PROGRAMMING III YEAR/II SEM MRCET Iteration: A loop statement allows us to execute a statement or group of statements multiple times as long as the condition is true. Repeated execution of a set of statements with the help of loops is called iteration. Loops statements are used when we need to run same code again and again, each time with a different value. Statements: In Python Iteration (Loops) statements are of three types: 1. While Loop 2. For Loop 3. Nested For Loops While loop: Loops are either infinite or conditional. Python while loop keeps reiterating a block of code defined inside it until the desired condition is met. The while loop contains a boolean expression and the code inside the loop is repeatedly executed as long as the boolean expression is true. The statements that are executed inside while can be a single line of code or a block of multiple statements. Syntax: while(expression): Statement(s) Flowchart: 41 PYTHON PROGRAMMING III YEAR/II SEM MRCET Example Programs: 1. -------------------------------------- i=1 while i> print absolute_value(0) None By the way, Python provides a built-in function called abs that computes absolute values. # Write a Python function that takes two lists and returns True if they have at least one common member. def common_data(list1, list2): for x in list1: for y in list2: if x == y: result = True return result print(common_data([1,2,3,4,5], [1,2,3,4,5])) print(common_data([1,2,3,4,5], [1,7,8,9,510])) print(common_data([1,2,3,4,5], [6,7,8,9,10])) Output: C:\Users\MRCET\AppData\Local\Programs\Python\Python38-32\pyyy\fu1.py 56 PYTHON PROGRAMMING III YEAR/II SEM MRCET True True None #----------------- def area(radius): b = 3.14159 * radius**2 return b Parameters: Parameters are passed during the definition of function while Arguments are passed during the function call. Example: #here a and b are parameters def add(a,b): #//function definition return a+b #12 and 13 are arguments #function call result=add(12,13) print(result) Output: C:/Users/MRCET/AppData/Local/Programs/Python/Python38-32/pyyy/paraarg.py 25 Some examples on functions: # To display vandemataram by using function use no args no return type #function defination def display(): print("vandemataram") print("i am in main") 57 PYTHON PROGRAMMING III YEAR/II SEM MRCET #function call display() print("i am in main") Output: C:/Users/MRCET/AppData/Local/Programs/Python/Python38-32/pyyy/fu1.py i am in main vandemataram i am in main #Type1 : No parameters and no return type def Fun1() : print("function 1") Fun1() Output: C:/Users/MRCET/AppData/Local/Programs/Python/Python38-32/pyyy/fu1.py function 1 #Type 2: with param with out return type def fun2(a) : print(a) fun2("hello") Output: C:/Users/MRCET/AppData/Local/Programs/Python/Python38-32/pyyy/fu1.py Hello #Type 3: without param with return type def fun3(): return "welcome to python" print(fun3()) 58 PYTHON PROGRAMMING III YEAR/II SEM MRCET Output: C:/Users/MRCET/AppData/Local/Programs/Python/Python38-32/pyyy/fu1.py welcome to python #Type 4: with param with return type def fun4(a): return a print(fun4("python is better then c")) Output: C:/Users/MRCET/AppData/Local/Programs/Python/Python38-32/pyyy/fu1.py python is better then c Local and Global scope: Local Scope: A variable which is defined inside a function is local to that function. It is accessible from the point at which it is defined until the end of the function, and exists for as long as the function is executing Global Scope: A variable which is defined in the main body of a file is called a global variable. It will be visible throughout the file, and also inside any file which imports that file. The variable defined inside a function can also be made global by using the global statement. def function_name(args):............. global x #declaring global variable inside a function.............. # create a global variable 59 PYTHON PROGRAMMING III YEAR/II SEM MRCET x = "global" def f(): print("x inside :", x) f() print("x outside:", x) Output: C:/Users/MRCET/AppData/Local/Programs/Python/Python38-32/pyyy/fu1.py x inside : global x outside: global # create a local variable def f1(): y = "local" print(y) f1() Output: local If we try to access the local variable outside the scope for example, def f2(): y = "local" f2() print(y) Then when we try to run it shows an error, Traceback (most recent call last): File "C:/Users/MRCET/AppData/Local/Programs/Python/Python38-32/pyyy/fu1.py", line 6, in 60 PYTHON PROGRAMMING III YEAR/II SEM MRCET print(y) NameError: name 'y' is not defined The output shows an error, because we are trying to access a local variable y in a global scope whereas the local variable only works inside f2() or local scope. # use local and global variables in same code x = "global" def f3(): global x y = "local" x=x*2 print(x) print(y) f3() Output: C:/Users/MRCET/AppData/Local/Programs/Python/Python38-32/pyyy/fu1.py globalglobal local In the above code, we declare x as a global and y as a local variable in the f3(). Then, we use multiplication operator * to modify the global variable x and we print both x and y. After calling the f3(), the value of x becomes global global because we used the x * 2 to print two times global. After that, we print the value of local variable y i.e local. # use Global variable and Local variable with same name x=5 def f4(): x = 10 print("local x:", x) f4() print("global x:", x) 61 PYTHON PROGRAMMING III YEAR/II SEM MRCET Output: C:/Users/MRCET/AppData/Local/Programs/Python/Python38-32/pyyy/fu1.py local x: 10 global x: 5 Function Composition: Having two (or more) functions where the output of one function is the input for another. So for example if you have two functions FunctionA and FunctionB you compose them by doing the following. FunctionB(FunctionA(x)) Here x is the input for FunctionA and the result of that is the input for FunctionB. Example 1: #create a function compose2 >>> def compose2(f, g): return lambda x:f(g(x)) >>> def d(x): return x*2 >>> def e(x): return x+1 >>> a=compose2(d,e) # FunctionC = compose(FunctionB,FunctionA) >>> a(5) # FunctionC(x) 12 In the above program we tried to compose n functions with the main function created. Example 2: >>> colors=('red','green','blue') >>> fruits=['orange','banana','cherry'] >>> zip(colors,fruits) 62 PYTHON PROGRAMMING III YEAR/II SEM MRCET >>> list(zip(colors,fruits)) [('red', 'orange'), ('green', 'banana'), ('blue', 'cherry')] Recursion: Recursion is the process of defining something in terms of itself. Python Recursive Function We know that in Python, a function can call other functions. It is even possible for the function to call itself. These type of construct are termed as recursive functions. Factorial of a number is the product of all the integers from 1 to that number. For example, the factorial of 6 (denoted as 6!) is 1*2*3*4*5*6 = 720. Following is an example of recursive function to find the factorial of an integer. # Write a program to factorial using recursion def fact(x): if x==0: result = 1 else : result = x * fact(x-1) return result print("zero factorial",fact(0)) print("five factorial",fact(5)) Output: C:/Users/MRCET/AppData/Local/Programs/Python/Python38-32/pyyy/rec.py zero factorial 1 five factorial 120 ---------------------- def calc_factorial(x): """This is a recursive function to find the factorial of an integer""" if x == 1: return 1 else: return (x * calc_factorial(x-1)) 63 PYTHON PROGRAMMING III YEAR/II SEM MRCET num = 4 print("The factorial of", num, "is", calc_factorial(num)) Output: C:/Users/MRCET/AppData/Local/Programs/Python/Python38-32/pyyy/rec.py The factorial of 4 is 24 Strings: A string is a group/ a sequence of characters. Since Python has no provision for arrays, we simply use strings. This is how we declare a string. We can use a pair of single or double quotes. Every string object is of the type ‘str’. >>> type("name") >>> name=str() >>> name '' >>> a=str('mrcet') >>> a 'mrcet' >>> a=str(mrcet) >>> a 'c' >>> fruit = 'banana' >>> letter = fruit The second statement selects character number 1 from fruit and assigns it to letter. The expression in brackets is called an index. The index indicates which character in the sequence we want String slices: A segment of a string is called a slice. Selecting a slice is similar to selecting a character: Subsets of strings can be taken using the slice operator ([ ] and [:]) with indexes starting at 0 in the beginning of the string and working their way from -1 at the end. Slice out substrings, sub lists, sub Tuples using index. Syntax:[Start: stop: steps] Slicing will start from index and will go up to stop in step of steps. Default value of start is 0, 64 PYTHON PROGRAMMING III YEAR/II SEM MRCET Stop is last index of list And for step default is 1 For example 1− str = 'Hello World!' print str # Prints complete string print str # Prints first character of the string print str[2:5] # Prints characters starting from 3rd to 5th print str[2:] # Prints string starting from 3rd character print str * 2 # Prints string two times print str + "TEST" # Prints concatenated string Output: Hello World! H llo llo World! Hello World!Hello World! Hello World!TEST Example 2: >>> x='computer' >>> x[1:4] 'omp' >>> x[1:6:2] 'opt' >>> x[3:] 65 PYTHON PROGRAMMING III YEAR/II SEM MRCET 'puter' >>> x[:5] 'compu' >>> x[-1] 'r' >>> x[-3:] 'ter' >>> x[:-2] 'comput' >>> x[::-2] 'rtpo' >>> x[::-1] 'retupmoc' Immutability: It is tempting to use the [] operator on the left side of an assignment, with the intention of changing a character in a string. For example: >>> greeting='mrcet college!' >>> greeting='n' TypeError: 'str' object does not support item assignment The reason for the error is that strings are immutable, which means we can’t change an existing string. The best we can do is creating a new string that is a variation on the original: >>> greeting = 'Hello, world!' >>> new_greeting = 'J' + greeting[1:] >>> new_greeting 'Jello, world!' Note: The plus (+) sign is the string concatenation operator and the asterisk (*) is the repetition operator 66 PYTHON PROGRAMMING III YEAR/II SEM MRCET String functions and methods: There are many methods to operate on String. S.no Method name Description 1. isalnum() Returns true if string has at least 1 character and all characters are alphanumeric and false otherwise. 2. isalpha() Returns true if string has at least 1 character and all characters are alphabetic and false otherwise. 3. isdigit() Returns true if string contains only digits and false otherwise. 4. islower() Returns true if string has at least 1 cased character and all cased characters are in lowercase and false otherwise. 5. isnumeric() Returns true if a string contains only numeric characters and false otherwise. 6. isspace() Returns true if string contains only whitespace characters and false otherwise. 7. istitle() Returns true if string is properly “titlecased” and false otherwise. 8. isupper() Returns true if string has at least one cased character and all cased characters are in uppercase and false otherwise. 9. replace(old, new Replaces all occurrences of old in string with new [, max]) or at most max occurrences if max given. 10. split() Splits string according to delimiter str (space if not provided) and returns list of substrings; 11. count() Occurrence of a string in another string 12. find() Finding the index of the first occurrence of a string in another string 13. swapcase() Converts lowercase letters in a string to uppercase and viceversa 14. startswith(str, Determines if string or a substring of string (if starting index beg=0,end=le beg and ending index end are given) starts with substring str; n(string)) returns true if so and false otherwise. Note: All the string methods will be returning either true or false as the result 1. isalnum(): 67 PYTHON PROGRAMMING III YEAR/II SEM MRCET Isalnum() method returns true if string has at least 1 character and all characters are alphanumeric and false otherwise. Syntax: String.isalnum() Example: >>> string="123alpha" >>> string.isalnum() True 2. isalpha(): isalpha() method returns true if string has at least 1 character and all characters are alphabetic and false otherwise. Syntax: String.isalpha() Example: >>> string="nikhil" >>> string.isalpha() True 3. isdigit(): isdigit() returns true if string contains only digits and false otherwise. Syntax: String.isdigit() Example: >>> string="123456789" >>> string.isdigit() True 4. islower(): Islower() returns true if string has characters that are in lowercase and false otherwise. Syntax: 68 PYTHON PROGRAMMING III YEAR/II SEM MRCET String.islower() Example: >>> string="nikhil" >>> string.islower() True 5. isnumeric(): isnumeric() method returns true if a string contains only numeric characters and false otherwise. Syntax: String.isnumeric() Example: >>> string="123456789" >>> string.isnumeric() True 6. isspace(): isspace() returns true if string contains only whitespace characters and false otherwise. Syntax: String.isspace() Example: >>> string=" " >>> string.isspace() True 7. istitle() istitle() method returns true if string is properly “titlecased”(starting letter of each word is capital) and false otherwise Syntax: String.istitle() 69 PYTHON PROGRAMMING III YEAR/II SEM MRCET Example: >>> string="Nikhil Is Learning" >>> string.istitle() True 8. isupper() isupper() returns true if string has characters that are in uppercase and false otherwise. Syntax: String.isupper() Example: >>> string="HELLO" >>> string.isupper() True 9. replace() replace() method replaces all occurrences of old in string with new or at most max occurrences if max given. Syntax: String.replace() Example: >>> string="Nikhil Is Learning" >>> string.replace('Nikhil','Neha') 'Neha Is Learning' 10.split() split() method splits the string according to delimiter str (space if not provided) Syntax: String.split() Example: >>> string="Nikhil Is Learning" >>> string.split() 70 PYTHON PROGRAMMING III YEAR/II SEM MRCET ['Nikhil', 'Is', 'Learning'] 11.count() count() method counts the occurrence of a string in another string Syntax: String.count() Example: >>> string='Nikhil Is Learning' >>> string.count('i') 3 12.find() Find() method is used for finding the index of the first occurrence of a string in another string Syntax: String.find(„string‟) Example: >>> string="Nikhil Is Learning" >>> string.find('k') 2 13.swapcase() converts lowercase letters in a string to uppercase and viceversa Syntax: String.find(„string‟) Example: >>> string="HELLO" >>> string.swapcase() 'hello' 14.startswith() Determines if string or a substring of string (if starting index beg and ending index end are given) starts with substring str; returns true if so and false otherwise. 71 PYTHON PROGRAMMING III YEAR/II SEM MRCET Syntax: String.startswith(„string‟) Example: >>> string="Nikhil Is Learning" >>> string.startswith('N') True 15.endswith() Determines if string or a substring of string (if starting index beg and ending index end are given) ends with substring str; returns true if so and false otherwise. Syntax: String.endswith(„string‟) Example: >>> string="Nikhil Is Learning" >>> string.startswith('g') True String module: This module contains a number of functions to process standard Python strings. In recent versions, most functions are available as string methods as well. It’s a built-in module and we have to import it before using any of its constants and classes Syntax: import string Note: help(string) --- gives the information about all the variables ,functions, attributes and classes to be used in string module. Example: import string print(string.ascii_letters) print(string.ascii_lowercase) print(string.ascii_uppercase) print(string.digits) 72 PYTHON PROGRAMMING III YEAR/II SEM MRCET print(string.hexdigits) #print(string.whitespace) print(string.punctuation) Output: C:/Users/MRCET/AppData/Local/Programs/Python/Python38-32/pyyy/strrmodl.py ========================================= abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ abcdefghijklmnopqrstuvwxyz ABCDEFGHIJKLMNOPQRSTUVWXYZ 0123456789 0123456789abcdefABCDEF !"#$%&'()*+,-./:;?@[\]^_`{|}~ Python String Module Classes Python string module contains two classes – Formatter and Template. Formatter It behaves exactly same as str.format() function. This class becomes useful if you want to subclass it and define your own format string syntax. Syntax: from string import Formatter Template This class is used to create a string template for simpler string substitutions Syntax: from string import Template Python arrays: Array is a container which can hold a fix number of items and these items should be of the same type. Most of the data structures make use of arrays to implement their algorithms. Following are the important terms to understand the concept of Array. Element− Each item stored in an array is called an element. Index − Each location of an element in an array has a numerical index, which is used to identify the element. Array Representation 73 PYTHON PROGRAMMING III YEAR/II SEM MRCET Arrays can be declared in various ways in different languages. Below is an illustration. Elements Int array = {10, 20, 30, 40, 50, 60, 70, 80, 85, 90} Type Name Size Index 0 As per the above illustration, following are the important points to be considered. Index starts with 0. Array length is 10 which means it can store 10 elements. Each element can be accessed via its index. For example, we can fetch an element at index 6 as 70 Basic Operations Following are the basic operations supported by an array. Traverse − print all the array elements one by one. Insertion − Adds an element at the given index. Deletion − Deletes an element at the given index. Search − Searches an element using the given index or by the value. Update − Updates an element at the given index. Array is created in Python by importing array module to the python program. Then the array is declared as shown below. from array import * arrayName=array(typecode, [initializers]) Typecode are the codes that are used to define the type of value the array will hold. Some common typecodes used are: Typecode Value b Represents signed integer of size 1 byte/td> B Represents unsigned integer of size 1 byte 74 PYTHON PROGRAMMING III YEAR/II SEM MRCET c Represents character of size 1 byte i Represents signed integer of size 2 bytes I Represents unsigned integer of size 2 bytes f Represents floating point of size 4 bytes d Represents floating point of size 8 bytes Creating an array: from array import * array1 = array('i', [10,20,30,40,50]) for x in array1: print(x) Output: >>> RESTART: C:/Users/MRCET/AppData/Local/Programs/Python/Python38-32/arr.py 10 20 30 40 50 Access the elements of an Array: Accessing Array Element We can access each element of an array using the index of the element. from array import * array1 = array('i', [10,20,30,40,50]) print (array1) print (array1) 75 PYTHON PROGRAMMING III YEAR/II SEM MRCET Output: RESTART: C:/Users/MRCET/AppData/Local/Programs/Python/Python38-32/pyyy/arr2.py 10 30 Array methods: Python has a set of built-in methods that you can use on lists/arrays. Method Description append() Adds an element at the end of the list clear() Removes all the elements from the list copy() Returns a copy of the list count() Returns the number of elements with the specified value extend() Add the elements of a list (or any iterable), to the end of the current list index() Returns the index of the first element with the specified value insert() Adds an element at the specified position pop() Removes the element at the specified position remove() Removes the first item with the specified value reverse() Reverses the order of the list sort() Sorts the list 76 PYTHON PROGRAMMING III YEAR/II SEM MRCET Note: Python does not have built-in support for Arrays, but Python Lists can be used instead. Example: >>> college=["mrcet","it","cse"] >>> college.append("autonomous") >>> college ['mrcet', 'it', 'cse', 'autonomous'] >>> college.append("eee") >>> college.append("ece") >>> college ['mrcet', 'it', 'cse', 'autonomous', 'eee', 'ece'] >>> college.pop() 'ece' >>> college ['mrcet', 'it', 'cse', 'autonomous', 'eee'] >>> college.pop(4) 'eee' >>> college ['mrcet', 'it', 'cse', 'autonomous'] >>> college.remove("it") >>> college ['mrcet', 'cse', 'autonomous'] 77 PYTHON PROGRAMMING III YEAR/II SEM MRCET UNIT – IV LISTS, TUPLES, DICTIONARIES Lists: list operations, list slices, list methods, list loop, mutability, aliasing, cloning lists, list parameters, list comprehension; Tuples: tuple assignment, tuple as return value, tuple comprehension; Dictionaries: operations and methods, comprehension; Lists, Tuples, Dictionaries: List: It is a general purpose most widely used in data structures List is a collection which is ordered and changeable and allows duplicate members. (Grow and shrink as needed, sequence type, sortable). To use a list, you must declare it first. Do this using square brackets and separate values with commas. We can construct / create list in many ways. Ex: >>> list1=[1,2,3,'A','B',7,8,[10,11]] >>> print(list1) [1, 2, 3, 'A', 'B', 7, 8, [10, 11]] ---------------------- >>> x=list() >>> x [] -------------------------- >>> tuple1=(1,2,3,4) >>> x=list(tuple1) >>> x [1, 2, 3, 4] 78 PYTHON PROGRAMMING III YEAR/II SEM MRCET List operations: These operations include indexing, slicing, adding, multiplying, and checking for membership Basic List Operations: Lists respond to the + and * operators much like strings; they mean concatenation and repetition here too, except that the result is a new list, not a string. Python Expression Results Description len([1, 2, 3]) 3 Length [1, 2, 3] + [4, 5, 6] [1, 2, 3, 4, 5, 6] Concatenation ['Hi!'] * 4 ['Hi!', 'Hi!', 'Hi!', 'Hi!'] Repetition 3 in [1, 2, 3] True Membership for x in [1, 2, 3]: print x, 123 Iteration Indexing, Slicing, and Matrixes Because lists are sequences, indexing and slicing work the same way for lists as they do for strings. Assuming following input − L = ['mrcet', 'college', 'MRCET!'] Python Expression Results Description L MRCET Offsets start at zero 79 PYTHON PROGRAMMING III YEAR/II SEM MRCET L[-2] college Negative: count from the right L[1:] ['college', 'MRCET!'] Slicing fetches sections List slices: >>> list1=range(1,6) >>> list1 range(1, 6) >>> print(list1) range(1, 6) >>> list1=[1,2,3,4,5,6,7,8,9,10] >>> list1[1:] [2, 3, 4, 5, 6, 7, 8, 9, 10] >>> list1[:1] >>> list1[2:5] [3, 4, 5] >>> list1[:6] [1, 2, 3, 4, 5, 6] >>> list1[1:2:4] >>> list1[1:8:2] [2, 4, 6, 8] List methods: The list data type has some more methods. Here are all of the methods of list objects: Del() 80 PYTHON PROGRAMMING III YEAR/II SEM MRCET Append() Extend() Insert() Pop() Remove() Reverse() Sort() Delete: Delete a list or an item from a list >>> x=[5,3,8,6] >>> del(x) #deletes the index position 1 in a list >>> x [5, 8, 6] ------------ >>> del(x) >>> x # complete list gets deleted Append: Append an item to a list >>> x=[1,5,8,4] >>> x.append(10) >>> x [1, 5, 8, 4, 10] Extend: Append a sequence to a list. >>> x=[1,2,3,4] >>> y=[3,6,9,1] >>> x.extend(y) >>> x [1, 2, 3, 4, 3, 6, 9, 1] Insert: To add an item at the specified index, use the insert () method: >>> x=[1,2,4,6,7] 81 PYTHON PROGRAMMING III YEAR/II SEM MRCET >>> x.insert(2,10) #insert(index no, item to be inserted) >>> x [1, 2, 10, 4, 6, 7] ------------------------- >>> x.insert(4,['a',11]) >>> x [1, 2, 10, 4, ['a', 11], 6, 7] Pop: The pop() method removes the specified index, (or the last item if index is not specified) or simply pops the last item of list and returns the item. >>> x=[1, 2, 10, 4, 6, 7] >>> x.pop() 7 >>> x [1, 2, 10, 4, 6] ----------------------------------- >>> x=[1, 2, 10, 4, 6] >>> x.pop(2) 10 >>> x [1, 2, 4, 6] Remove: The remove() method removes the specified item from a given list. >>> x=[1,33,2,10,4,6] >>> x.remove(33) >>> x 82 PYTHON PROGRAMMING III YEAR/II SEM MRCET [1, 2, 10, 4, 6] >>> x.remove(4) >>> x [1, 2, 10, 6] Reverse: Reverse the order of a given list. >>> x=[1,2,3,4,5,6,7] >>> x.reverse() >>> x [7, 6, 5, 4, 3, 2, 1] Sort: Sorts the elements in ascending order >>> x=[7, 6, 5, 4, 3, 2, 1] >>> x.sort() >>> x [1, 2, 3, 4, 5, 6, 7] ----------------------- >>> x=[10,1,5,3,8,7] >>> x.sort() >>> x [1, 3, 5, 7, 8, 10] List loop: Loops are control structures used to repeat a given section of code a certain number of times or until a particular condition is met. Method #1: For loop #list of items list = ['M','R','C','E','T'] 83 PYTHON PROGRAMMING III YEAR/II SEM MRCET i=1 #Iterating over the list for item in list: print ('college ',i,' is ',item) i = i+1 Output: C:/Users/MRCET/AppData/Local/Programs/Python/Python38-32/pyyy/lis.py college 1 is M college 2 is R college 3 is C college 4 is E college 5 is T Method #2: For loop and range() In case we want to use the traditional for loop which iterates from number x to number y. # Python3 code to iterate over a list list = [1, 3, 5, 7, 9] # getting length of list length = len(list) # Iterating the index # same as 'for i in range(len(list))' for i in range(length): print(list[i]) Output: C:/Users/MRCET/AppData/Local/Programs/Python/Python38-32/pyyy/listlooop.py 1 3 5 7 9 Method #3: using while loop # Python3 code to iterate over a list list = [1, 3, 5, 7, 9] # Getting length of list 84 PYTHON PROGRAMMING III YEAR/II SEM MRCET length = len(list) i=0 # Iterating using while loop while i < length: print(list[i]) i += 1 Mutability: A mutable object can be changed after it is created, and an immutable object can't. Append: Append an item to a list >>> x=[1,5,8,4] >>> x.append(10) >>> x [1, 5, 8, 4, 10] Extend: Append a sequence to a list. >>> x=[1,2,3,4] >>> y=[3,6,9,1] >>> x.extend(y) >>> x Delete: Delete a list or an item from a list >>> x=[5,3,8,6] >>> del(x) #deletes the index position 1 in a list >>> x [5, 8, 6] Insert: To add an item at the specified index, use the insert () method: >>> x=[1,2,4,6,7] >>> x.insert(2,10) #insert(index no, item to be inserted) 85 PYTHON PROGRAMMING III YEAR/II SEM MRCET >>> x [1, 2, 10, 4, 6, 7] ------------------------- >>> x.insert(4,['a',11]) >>> x [1, 2, 10, 4, ['a', 11], 6, 7] Pop: The pop() method removes the specified index, (or the last item if index is not specified) or simply pops the last item of list and returns the item. >>> x=[1, 2, 10, 4, 6, 7] >>> x.pop() 7 >>> x [1, 2, 10, 4, 6] ----------------------------------- >>> x=[1, 2, 10, 4, 6] >>> x.pop(2) 10 >>> x [1, 2, 4, 6] Remove: The remove() method removes the specified item from a given list. >>> x=[1,33,2,10,4,6] >>> x.remove(33) >>> x [1, 2, 10, 4, 6] 86 PYTHON PROGRAMMING III YEAR/II SEM MRCET >>> x.remove(4) >>> x [1, 2, 10, 6] Reverse: Reverse the order of a given list. >>> x=[1,2,3,4,5,6,7] >>> x.reverse() >>> x [7, 6, 5, 4, 3, 2, 1] Sort: Sorts the elements in ascending order >>> x=[7, 6, 5, 4, 3, 2, 1] >>> x.sort() >>> x [1, 2, 3, 4, 5, 6, 7] ----------------------- >>> x=[10,1,5,3,8,7] >>> x.sort() >>> x [1, 3, 5, 7, 8, 10] Aliasing: 1. An alias is a second name for a piece of data, often easier (and more useful) than making a copy. 2. If the data is immutable, aliases don’t matter because the data can’t change. 3. But if data can change, aliases can result in lot of hard – to – find bugs. 4. Aliasing happens whenever one variable’s value is assigned to another variable. For ex: a = [81, 82, 83] 87 PYTHON PROGRAMMING III YEAR/II SEM MRCET b = [81, 82, 83] print(a == b) print(a is b) b=a print(a == b) print(a is b) b = 5 print(a) Output: C:/Users/MRCET/AppData/Local/Programs/Python/Python38-32/pyyy/alia.py True False True True [5, 82, 83] Because the same list has two different names, a and b, we say that it is aliased. Changes made with one alias affect the other. In the example above, you can see that a and b refer to the same list after executing the assignment statement b = a. Cloning Lists: If we want to modify a list and also keep a copy of the original, we need to be able to make a copy of the list itself, not just the reference. This process is sometimes called cloning, to avoid the ambiguity of the word copy. The easiest way to clone a list is to use the slice operator. Taking any slice of a creates a new list. In this case the slice happens to consist of the whole list. Example: a = [81, 82, 83] b = a[:] # make a clone using slice print(a == b) print(a is b) b = 5 print(a) print(b) 88 PYTHON PROGRAMMING III YEAR/II SEM MRCET Output: C:/Users/MRCET/AppData/Local/Programs/Python/Python38-32/pyyy/clo.py True False [81, 82, 83] [5, 82, 83] Now we are free to make changes to b without worrying about a List parameters: Passing a list as an argument actually passes a reference to the list, not a copy of the list. Since lists are mutable, changes made to the elements referenced by the parameter change the same list that the argument is referencing. # for example, the function below takes a list as an argument and multiplies each element in the list by 2: def doubleStuff(List): """ Overwrite each element in aList with double its value. """ for position in range(len(List)): List[position] = 2 * List[position] things = [2, 5, 9] print(things) doubleStuff(things) print(things) Output: C:/Users/MRCET/AppData/Local/Programs/Python/Python38-32/lipar.py == [2, 5, 9] [4, 10, 18] 89 PYTHON PROGRAMMING III YEAR/II SEM MRCET List comprehension: List: List comprehensions provide a concise way to create lists. Common applications are to make new lists where each element is the result of some operations applied to each member of another sequence or iterable, or to create a subsequence of those elements that satisfy a certain condition. For example, assume we want to create a list of squares, like: >>> list1=[] >>> for x in range(10): list1.append(x**2) >>> list1 [0, 1, 4, 9, 16, 25, 36, 49, 64, 81] (or) This is also equivalent to >>> list1=list(map(lambda x:x**2, range(10))) >>> list1 [0, 1, 4, 9, 16, 25, 36, 49, 64, 81] (or) Which is more concise and redable. >>> list1=[x**2 for x in range(10)] >>> list1 [0, 1, 4, 9, 16, 25, 36, 49, 64, 81] 90 PYTHON PROGRAMMING III YEAR/II SEM MRCET Similarily some examples: >>> x=[m for m in range(8)] >>> print(x) [0, 1, 2, 3, 4, 5, 6, 7] >>> x=[z**2 for z in range(10) if z>4] >>> print(x) [25, 36, 49, 64, 81] >>> x=[x ** 2 for x in range (1, 11) if x % 2 == 1] >>> print(x) [1, 9, 25, 49, 81] >>> a=5 >>> table = [[a, b, a * b] for b in range(1, 11)] >>> for i in table: print(i) [5, 1, 5] [5, 2, 10] [5, 3, 15] [5, 4, 20] [5, 5, 25] [5, 6, 30] [5, 7, 35] [5, 8, 40] [5, 9, 45] [5, 10, 50] Tuples: A tuple is a collection which is ordered and unchangeable. In Python tuples are written with round brackets. Supports all operations for sequences. Immutable, but member objects may be mutable. If the contents of a list shouldn’t change, use a tuple to prevent items from 91 PYTHON PROGRAMMING III YEAR/II SEM MRCET accidently being added, changed, or deleted. Tuples are more efficient than list due to python’s implementation. We can construct tuple in many ways: X=() #no item tuple X=(1,2,3) X=tuple(list1) X=1,2,3,4 Example: >>> x=(1,2,3) >>> print(x) (1, 2, 3) >>> x (1, 2, 3) ----------------------- >>> x=() >>> x () ---------------------------- >>> x=[4,5,66,9] >>> y=tuple(x) >>> y (4, 5, 66, 9) ----------------------------- >>> x=1,2,3,4 >>> x (1, 2, 3, 4) Some of the operations of tuple are: Access tuple items Change tuple items Loop through a tuple Count() Index() Length() 92 PYTHON PROGRAMMING III YEAR/II SEM MRCET Access tuple items: Access tuple items by referring to the index number, inside square brackets >>> x=('a','b','c','g') >>> print(x) c Change tuple items: Once a tuple is created, you cannot change its values. Tuples are unchangeable. >>> x=(2,5,7,'4',8) >>> x=10 Traceback (most recent call last): File "", line 1, in x=10 TypeError: 'tuple' object does not support item assignment >>> x (2, 5, 7, '4', 8) # the value is still the same Loop through a tuple: We can loop the values of tuple using for loop >>> x=4,5,6,7,2,'aa' >>> for i in x: print(i) 4 5 6 7 2 aa Count (): Returns the number of times a specified value occurs in a tuple >>> x=(1,2,3,4,5,6,2,10,2,11,12,2) >>> x.count(2) 4 Index (): Searches the tuple for a specified value and returns the position of where it was found 93 PYTHON PROGRAMMING III YEAR/II SEM MRCET >>> x=(1,2,3,4,5,6,2,10,2,11,12,2) >>> x.index(2) 1 (Or) >>> x=(1,2,3,4,5,6,2,10,2,11,12,2) >>> y=x.index(2) >>> print(y) 1 Length (): To know the number of items or values present in a tuple, we use len(). >>> x=(1,2,3,4,5,6,2,10,2,11,12,2) >>> y=len(x) >>> print(y) 12 Tuple Assignment Python has tuple assignment feature which enables you to assign more than one variable at a time. In here, we have assigned tuple 1 with the college information like college name, year, etc. and another tuple 2 with the values in it like number (1, 2, 3… 7). For Example, Here is the code, >>> tup1 = ('mrcet', 'eng college','2004','cse', 'it','csit'); >>> tup2 = (1,2,3,4,5,6,7); >>> print(tup1) mrcet >>> print(tup2[1:4]) (2, 3, 4) Tuple 1 includes list of information of mrcet Tuple 2 includes list of numbers in it 94 PYTHON PROGRAMMING III YEAR/II SEM MRCET We call the value for in tuple and for tuple 2 we call the value between 1 and 4 Run the above code- It gives name mrcet for first tuple while for second tuple it gives number (2, 3, 4) Tuple as return values: A Tuple is a comma separated sequence of items. It is created with or without (). Tuples are immutable. # A Python program to return multiple values from a method using tuple # This function returns a tuple def fun(): str = "mrcet college" x = 20 return str, x; # Return tuple, we could also # write (str, x) # Driver code to test above method str, x = fun() # Assign returned tuple print(str) print(x) Output: C:/Users/MRCET/AppData/Local/Programs/Python/Python38-32/tupretval.py mrcet college 20 Functions can return tuples as return values. def circleInfo(r): """ Return (circumference, area) of a circle of radius r """ c = 2 * 3.14159 * r a = 3.14159 * r * r return (c, a) print(circleInfo(10)) Output: C:/Users/MRCET/AppData/Local/Programs/Python/Python38-32/functupretval.py (62.8318, 314.159) 95 PYTHON PROGRAMMING III YEAR/II SEM MRCET ------------------------------ def f(x): y0 = x + 1 y1 = x * 3 y2 = y0 ** y3 return (y0, y1, y2) Tuple comprehension: Tuple Comprehensions are special: The result of a tuple comprehension is special. You might expect it to produce a tuple, but what it does is produce a special "generator" object that we can iterate over. For example: >>> x = (i for i in 'abc') #tuple comprehension >>> x >>> print(x) You might expect this to print as ('a', 'b', 'c') but it prints as The result of a tuple comprehension is not a tuple: it is actually a generator. The only thing that you need to know now about a generator now is that you can iterate over it, but ONLY ONCE. So, given the code >>> x = (i for i in 'abc') >>> for i in x: print(i) a b c Create a list of 2-tuples like (number, square): >>> z=[(x, x**2) for x in range(6)] >>> z [(0, 0), (1, 1), (2, 4), (3, 9), (4, 16), (5, 25)] 96 PYTHON PROGRAMMING III YEAR/II SEM MRCET Set: Similarly to list comprehensions, set comprehensions are also supported: >>> a = {x for x in 'abracadabra' if x not in 'abc'} >>> a {'r', 'd'} >>> x={3*x for x in range(10) if x>5} >>> x {24, 18, 27, 21} Dictionaries: A dictionary is a collection which is unordered, changeable and indexed. In Python dictionaries are written with curly brackets, and they have keys and values. Key-value pairs Unordered We can construct or create dictionary like: X={1:’A’,2:’B’,3:’c’} X=dict([(‘a’,3) (‘b’,4)] X=dict(‘A’=1,’B’ =2) Example: >>> dict1 = {"brand":"mrcet","model":"college","year":2004} >>> dict1 {'brand': 'mrcet', 'model': 'college', 'year': 2004} Operations and methods: Methods that are available with dictionary are tabulated below. Some of them have already been used in the above examples. Method Description clear() Remove all items form the dictionary. 97 PYTHON PROGRAMMING III YEAR/II SEM MRCET copy() Return a shallow copy of the dictionary. Return a new dictionary with keys from seq and fromkeys(seq[, v]) value equal to v (defaults to None). Return the value of key. If key doesnot exit, get(key[,d]) return d (defaults to None). Return a new view of the dictionary's items items() (key, value). keys() Return a new view of the dictionary's keys. Remove the item with key and return its value or d if key is not found. If d is not provided pop(key[,d]) and key is not found, raises KeyError. Remove and return an arbitary item (key, value). Raises KeyError if the dictionary is popitem() empty. If key is in the dictionary, return its value. If not, insert key with a value of d and setdefault(key[,d]) return d (defaults to None). Update the dictionary with the key/value pairs update([other]) from other, overwriting existing keys. values() Return a new view of the dictionary's values Below are some dictionary operations: 98 PYTHON PROGRAMMING III YEAR/II SEM MRCET To access specific value of a dictionary, we must pass its key, >>> dict1 = {"brand":"mrcet","model":"college","year":2004} >>> x=dict1["brand"] >>> x 'mrcet' --------------------- To access keys and values and items of dictionary: >>> dict1 = {"brand":"mrcet","model":"college","year":2004} >>> dict1.keys() dict_keys(['brand', 'model', 'year']) >>> dict1.values() dict_values(['mrcet', 'college', 2004]) >>> dict1.items() dict_items([('brand', 'mrcet'), ('model', 'college'), ('year', 2004)]) ----------------------------------------------- >>> for items in dict1.values(): print(items) mrcet college 2004 >>> for items in dict1.keys(): print(items) brand model year >>> for i in dict1.items(): print(i) ('brand', 'mrcet') ('model', 'college') ('year', 2004) Some more operations like: Add/change 99 PYTHON PROGRAMMING III YEAR/II SEM MRCET Remove Length Delete Add/change values: You can change the value of a specific item by referring to its key name >>> dict1 = {"brand":"mrcet","model":"college","year":2004} >>> dict1["year"]=2005 >>> dict1 {'brand': 'mrcet', 'model': 'college', 'year': 2005} Remove(): It removes or pop the specific item of dictionary. >>> dict1 = {"brand":"mrcet","model":"college","year":2004} >>> print(dict1.pop("model")) college >>> dict1 {'brand': 'mrcet', 'year': 2005} Delete: Deletes a particular item. >>> x = {1:1, 2:4, 3:9, 4:16, 5:25} >>> del x >>> x Length: we use len() method to get the length of dictionary. >>>{1: 1, 2: 4, 3: 9, 4: 16} {1: 1, 2: 4, 3: 9, 4: 16} >>> y=len(x) >>> y 4 Iterating over (key, value) pairs: >>> x = {1:1, 2:4, 3:9, 4:16, 5:25} >>> for key in x: print(key, x[key]) 11 24 39 100 PYTHON PROGRAMMING III YEAR/II SEM MRCET 4 16 5 25 >>> for k,v in x.items(): print(k,v) 11 24 39 4 16 5 25 List of Dictionaries: >>> customers = [{"uid":1,"name":"John"}, {"uid":2,"name":"Smith"}, {"uid":3,"name":"Andersson"}, ] >>> >>> print(customers) [{'uid': 1, 'name': 'John'}, {'uid': 2, 'name': 'Smith'}, {'uid': 3, 'name': 'Andersson'}] ## Print the uid and name of each customer >>> for x in customers: print(x["uid"], x["name"]) 1 John 2 Smith 3 Andersson ## Modify an entry, This will change the name of customer 2 from Smith to Charlie >>> customers["name"]="charlie" >>> print(customers) [{'uid': 1, 'name': 'John'}, {'uid': 2, 'name': 'Smith'}, {'uid': 3, 'name': 'charlie'}] ## Add a new field to each entry >>> for x in customers: x["password"]="123456" # any initial value >>> print(customers) 101 PYTHON PROGRAMMING III YEAR/II SEM MRCET [{'uid': 1, 'name': 'John', 'password': '123456'}, {'uid': 2, 'name': 'Smith', 'password': '123456'}, {'uid': 3, 'name': 'charlie', 'password': '123456'}] ## Delete a field >>> del customers >>> print(customers) [{'uid': 1, 'name': 'John', 'password': '123456'}, {'uid': 3, 'name': 'charlie', 'password': '123456'}] >>> del customers >>> print(customers) [{'uid': 1, 'name': 'John', 'password': '123456'}] ## Delete all fields >>> for x in
