Python Programming Fundamentals

• The content covers fundamentals of Python programming.

Why Python?

• Python is object-oriented and supports polymorphism, operation overloading, and multiple inheritance.
• Python is open source, free, and easy to install, with accessible source code and a large online community.
• Python is portable and runs on most major platforms, requiring a compatible Python interpreter to execute programs uniformly across platforms.
• Python is powerful due to dynamic typing, built-in types/tools, library utilities, third-party utilities (Numeric, NumPy, SciPy), and automatic memory management.

Python IDLE

• IDLE stands for Integrated Development Environment.
• After installing IDLE, users can begin writing Python programs.

Programming Modes

• Interactive Mode: Provides immediate feedback, but isn't designed for saving programs.
• Script Mode: Enables writing, editing, saving, and running programs, which should besaved with a ".py" extension.

Creating and Running Programs in Script Mode

• To create and run programs: Go to File menu, create a new file, name it with ".py" extension (ex: firstProgram.py), write code, save, and run via Run menu -> Run Module or press F5.

Program Development Cycle

• Programs need careful design before coding.
• Programmers utilize tools like pseudocode/flowcharts for modeling.
• A program often needs 5 phases shown to work properly.
• The entire process is named the program development cycle.

Program Development Cycle Phases

• Design: Programs should be carefully designed before coding.
• Code: After designing, write code in a high-level language such as Python, considering syntax.
• Correct Syntax Errors: The compiler/interpreter shows an error message for syntax errors.
• Test the Program: Test executable code to identify logic errors, which don't prevent running but cause incorrect results.
• Correct Logic Errors: Debug the code if it produces incorrect results.

Data Types

• Integer: Positive or negative whole numbers without decimals.
• Float: Real numbers with a decimal point, including scientific notation (e.g., 2.5e2 = 250).
• Complex: Numbers in the form a + bJ, where J or j represents the square root of -1; a is the real part, b is the imaginary part.
• Boolean: Represents either True or False; used to compare values.

Strings

• Strings: Created using single, double, or triple quotes.
• Sequence Types: Lists, tuples, and ranges (discussed later).
• Two consecutive equal marks operator (==) returns true if both operands have the same value; otherwise, it returns false.

Python print() Function

• Functions are reusable code that performs operations.
• The print() function displays messages on the screen.
• Messages can be strings or other objects converted to strings.
• Sequences of characters can serve as data, it is called a string.
• Strings that appear directly in the code is named "string literal".
• String literals must be enclosed in quotation marks.
• Literals are numbers or strings that appear directly in a program

First Python Program

• Python is case-sensitive. "print("hello")" is correct, but "Print("hello")" generates an error.
• "hello" is an example of a string literal.
• Computers generate a syntax error if the statement isn't recognized.

String Literals

• String literals are immutable, meaning their content cannot be altered after creation.
• Strings are enclosed in single or double quotation marks, which are interchangeable, where 'hello' is the same as "hello".
• String content can be shown on the screen with print("hello").
• Use double quotes ("Don't panic!") to include a single quote/apostrophe.

String Literals (cont.)

• Python strings are arrays of bytes representing Unicode characters; Python lacks a character data type as a single character is just a string of length 1.
• Square brackets are usable to access string elements.
• To get the first character of a string (In Python, the 1st character has position 0).
• The len() function will return the length of a string.

String literals (cont.)

• The keyword in can check if a phrase or character exists inside a string.
• Slicing can return a range of characters.
• The slicing format is string[start:stop:step].
• Slicing returns string characters from start up to, but not including, stop and the step determines steps to take from start to stop (exclusive).

String Literals (Indexes)

• Negative indexes can be utilized to start slicing a string from the end.

Print Function: Overpowering the print Function's Ending

• By default, there is a newline character \n at the end.
• You can end a print statement with any character or string using the parameter end.
• To specify no space between the quote marks, indicate that the print function prints nothing at the end of output.

Print Function: Specifying an Item Separator

• When having multiple arguments for the print function, the function will automatically display a space.
• sep="" will display nothing in the space.

The Print Function: Escape Characters

• An escape character is preceded by a backslash () inside a string literal and acts as a special command.
• \n: Advances output to the next line.
• \t: Skips to the next horizontal tab.
• \': Prints a single quote.
• \": Prints a double quote.
• \\: Prints a backslash.

Displaying Multiple Items with the + Operator

• + performs string concatenation.

Formatting Numbers

• Floating-point numbers support up to 12 significant digits.
• The format function will pass two arguments; formatting rules and a value.

Program Documentation

• Comments are notes explaining sections which are ignored by the computer.
• The "#" indicates the start of a comment.

Variables

• Variables save a name that is a value stored in computer's memory, where a user can reused the values in multiple places.
• Programs will use variables to work with the data that is stored in the memory.
• An assignment statement is need for defining the variable which is variable = expression.

Variables

• Assign values to multiple variables simultaneously.
• Variable names can include letters, numbers, and underscores (excluding the dollar sign).
• Variable names should not have spaces and can't start with a number.
• Variable names cannot be reserved and are case-sensitive ("temp" and "Temp" are different).

Variables Rules

• It's important to avoid using a variable before it's assigned a value because it may cause an error.

Displaying Multiple Items

• Python can display multiple items with one call to print, separating the items with commas.

Reading From the Keyboard

• Use the input function and an assignment statement to read from user keyboard.
• The function eval() will convert from strings to numeric values.
• Important: Using a variable before assigned to it is invalid.

Math Operators

• + Addition, can be used for string concatenation.
• - Subtraction.
• * Multiplication, can be used for string repetition.
• / Float division.
• // Integer division.
• ** Exponentiation.
• % Remainder.

Operator Precedence

• You can write complex mathematical expressions with multiple operators.
• Operators enclosed in parentheses are applied first.
• If two operators share an operand, the operator with the higher precedence is applied.
• Parts of mathematical expressions can be grouped to force operation order.

Casting

• The order of math operators from highest to lowest are Parentheses, Exponentiation, Multiplication/Division/Remainder, Addition, and Subtraction
• Python implicitly converts numbers in mixed-type expressions.
• Casting, also called type conversion, explicitly converts between types:
  • int(x): Converts x to an integer.
  • float(x): Converts x to a float.
  • str(): Constructs a string from various data types.
  • complex(x): Converts x to a complex number; the imaginary part is zero.
  • complex(x, y): Converts x and y to a complex number.

Casting in Python (Examples)

• If a string is named '100', after converting to a number with int(x) you can compute mathematical operations.

Casting to strings (examples)

• To cast "s1" to a string, str("s1") will yield 's1'.

String Testing Methods

• isalnum()- Returns True if the string is letters/digits and at least one character, else False.
• isalpha() - Returns True if the string has letters and is at least one character, else False.
• isdigit() - Returns True if the the string is numeric digits is at least one character, else False.
• islower()- Returns True if all letters in the string are lowercase and at least one alphabetic letter, or False otherwise.
• isspace()- Returns True if the a character/length is whitespace and at least one character, else False.
• isupper()- Returns True if alphabetic letters of a string is uppercase and one alphabetic letter, and returns False otherwise.

String Modification Methods

• These return the modified version:
  • lower(): Converts to lowercase.
  • lstrip(): Removes leading whitespace.
  • lstrip(char): Removes leading instances of a character.
  • rstrip(): Removes trailing whitespace.
  • rstrip(char): Removes trailing instances.
  • strip(): Removes both leading and trailing whitespaces.
  • strip(char): Removes instances from both ends.
  • upper(): Converts to uppercase.