Lecture 1 Introduction to Python Programming PDF

CSCI 101: Introduction to Computer Science Lecture 01: First Program  Agenda ▪ Computer hardware and software ▪ How to write a program? ▪ Substitution in mathematics & programming ▪ Building our first program ▪ Memory ▪ Getting input / Displaying output ▪ Ar...

CSCI 101: Introduction to Computer Science Lecture 01: First Program  Agenda ▪ Computer hardware and software ▪ How to write a program? ▪ Substitution in mathematics & programming ▪ Building our first program ▪ Memory ▪ Getting input / Displaying output ▪ Arithmetic expressions ▪ Sample programs Computer Hardware Processor  Computer Hardware ▪ Input Unit: accepts inputs from users, translates it, and transmits it to the processor (e.g. keyboard, joystick, microphone and mouse) ▪ Output Unit: display processed information to the outside world (e.g. monitors, printers (2D and 3D), speakers, and projectors) ▪ Arithmetic and Logic Unit: calculates arithmetic and logical expressions. It reads the operands from memory, perform the operation and store the resultant value in memory. ▪ Memory Unit: stores programs and data (two classes primary and secondary) ▪ Control unit : coordinates the operation of all other units. It is the nerve center that sends control signals to all units and senses their status.  Software Program ▪ A computer can perform a specific set of instructions, one at a time. ▪ Get input (from keyboard to memory) ▪ Display output (from memory to screen) ▪ Compute an arithmetic expression (*, /, +, -) ▪ Compute a logical expression and branch selection ▪ Repeat instructions ▪ A software program is a sequence of such instructions  Cooking Introduction to Computer Science  Introduction to Cooking Science ▪ Cooking recipes can be thought of as simple algorithms Omelette recipe: 1. Break 2 eggs in the bowl 2. Put grains of salt in the bowl 3. Mix together in the bowl ▪ Common between recipes and algorithms: 4. Pour in a hot pan ▪ Sequence of steps ▪ Performing step 3 means steps 1 and 2 are complete ▪ Has order, changing order MAY ruin it: ▪ Examples: ▪ Swap steps 1 and 2? ▪ Swap steps 2 and 3? ▪ Swap steps 3 and 4? ▪ Dependencies (building on previous steps) is the key to determine the order  Introduction to Cooking Science Omelette recipe: 1. Break 2 eggs in the bowl 2. Put grains of salt in the bowl 3. Mix together in the bowl 4. Pour in a hot pan ▪ Add more complexity: keep mixing together till the mixture is homogeneous. ▪ Use what is called while loop that repeats as long as a condition is valid (True) Omelette recipe: 1. Break 2 eggs in the bowl 2. Put grains of salt in the bowl The condition that must remain valid for a 3. While not well mixed: while loop to keep iterating / repeating i. Mix together in the bowl 4. Pour in a hot pan  Introduction to Cooking Science ▪ What if we want to make 5 Omelette plates? ▪ Repeat the recipe 5 times Omelette recipe: 1. Repeat 5 times: Count (number of iterations) i. Break 2 eggs in the bowl ii. Put grains of salt in the bowl iii. While not well mixed: a. Mix together in the bowl iv. Pour in a hot pan ▪ Called for loop and must repeat for a known number of times  But… ▪ The previous recipes must be taken with grains of salt!! Omelette recipe: 1. Repeat 5 times: ▪ These steps are not accurate enough, the i. Break 2 eggs in the bowl output can be different based on the ii. Put grains of salt in the bowl iii. While not well mixed: executer: a. Mix together in the bowl iv. Pour in a hot pan ▪ How much salt?!! ▪ How well mixed is enough?!! ▪ How hot is the pan?! ▪ An algorithm must obtain the same expected correct output every run.  How to write a software program? 1. Read the problem statement, and identify ▪ The input and its range ▪ The output ▪ The relationship between the input and the output (how to compute the output) [Comprehend or understood] 2. Write your thoughts as a sequence of steps. [Algorithm] 3. Convert these steps to Code. [Program] 4. Test your code and compare your program result against a human result. [Testing]  Writing a Computer Program: The Role of Algorithms ▪ An algorithm is a set of steps that describes how a task can be performed (informal definition). ▪ Fundamental concept of computer science ▪ The word is derived from the famous mathematician Muḥammad ibn Musa al-Khwarizmi, one of the first Directors of the House of Wisdom (a major public academy and intellectual center), in Bagdad (9th century). ▪ Began as a subject in mathematics. The goal was to find a single set of directions that describes how all problems of a particular type could be solved. ▪ “If no algorithm exists for solving a problem, then the solution of that problem lies beyond the capabilities of machines.” 1. From the book “Computer Science: an overview” by J. Glenn Brookshear  Algorithms: Formal Definition ▪ An algorithm is an ordered set of unambiguous, executable steps that defines a terminating process. ▪ Ordered: Steps are executed in a sequence. (In parallel algorithms, we may have more than one execution path) ▪ Unambiguous: A single and unique interpretation. The information must be sufficient to determine uniquely and completely the required actions. ▪ Branch if the value of x is large enough. Is it unambiguous? ▪ Some algorithms (nondeterministic algorithms) do not conform to this restriction. ▪ Executable: A step that can be done. ▪ Make a list of all the positive integers. Is it executable ▪ Terminating: the execution must lead to an end. ▪ There are, however, some meaningful non-terminating processes such as monitoring the vital signs of a patient. 1. From the book “Computer Science: an overview” by J. Glenn Brookshear  Algorithm Representation ▪ Pseudocode: ▪ An intuitive notational system in which ideas can be expressed informally. ▪ Less formal than target programming language. ▪ Flexible, less complex, and easy to understand compared to formal programming languages. ▪ Flowchart: ▪ A graphical representation of an algorithm. ▪ Provides a simple way to visualize transitions and analyze the execution paths.  Pseudocode: Examples ▪ Write an algorithm to calculate the area of a circle ▪ Determine inputs, outputs, and relation ▪ Step 1: Get Radius from user ▪ Step 2: Set Pi = 3.14 ▪ Step 3: Calculate Area = Pi * Radius * Radius ▪ Step 4: Print Area  Pseudocode: Examples ▪ Write an algorithm to convert temperature from Fahrenheit to Celsius ▪ Determine inputs, outputs, and relation T(°C) = (T(°F) - 32) × 5/9 ▪ Step 1: Get Temp in Fahrenheit (F) from user ▪ Step 2: Calculate C = 5/9 * (F-32) ▪ Step 3: Print C  Exercise ▪ Find 𝑿𝟐 and 𝑿𝟑 of any given number X ▪ Determine inputs, outputs, and relation ▪ Step 1: Get X from user ▪ Step 2: Set XSquare = X * X ▪ Step 3: Set XCube = XSquare * X ▪ Step 4: Print XSquare, XCube  Substitution in Mathematics & Programming ▪ Software evolved first to serve solving mathematical problems. ▪ Therefore, it follows the main concepts of evaluating expressions ▪ Substitution in mathematical expressions works the same way in code  Substitution in Mathematics & Programming 𝑥=4 𝑥 𝑦=𝑒 ▪ Solving the above mathematically by substituting manually step by step: 4 𝑦=𝑒 𝑦 = 𝑒2 𝑦 = 2.7182 𝑦 = 7.38  Substitution in Mathematics & Programming import the library called ▪ In Python, it is written as: import math math which contains x = 4 mathematical functions ▪ By substituting step by step: y = math.exp(math.sqrt(x)) Refer to the library 1. First 4 is assigned to x before calling any function from inside it 2. Then x is substituted for, y = math.exp(math.sqrt(4)) 3. Function math.sqrt(4) is called which takes 4 as an input, gets evaluated and returns back 2, now y = math.exp(2) 4. Function math.exp(2) is called which takes 2 as an input, gets evaluated and returns back 7.38 which gets assigned to y Exercise: x = 4 y = math.cos(math.exp(x/2-2)*math.pi)/math.sin(math.pi/2)  Memory ▪ Memory is divided into bytes x 15 y 12 ▪ Each byte has its own address represented by binary numbers sum 45 A 2 A1 -3 ▪ 4 or 8 bytes form a memory location to store integer or floating (Ex 10.2345) numbers numOfBus 4 ▪ Software programs use letters and numbers to name the memory location.  Memory Location Name (Variables) ▪ Variable: a named space for storing a value radius ▪ Valid names: ▪ Must start with a letter or ‘_’ , ▪ Can contain any combination of letters, digits, or ‘_’. ▪ Use meaningful variable names (avoid reserved words). ▪ Python (as well as most others) is case sensitive (area and Area are different) ▪ Exercise Xyz 3xyz x-y ab2cd a12345 myvar AbCdE1234  Variable Types ▪ Integer: ▪ x = 4 ▪ y = x * 2 ▪ Using substitution, y = ? ▪ type(x) Built in function to returns the type of the object ▪ type(y) ▪ type(x * 2) ▪ Again follow substitution  Variable Types ▪ Float/decimal: ▪ x = 4.0 ▪ y = x * 2 ▪ Using substitution, y = ? ▪ type(x) ▪ type(y) ▪ type(x * 2)  Variable Types ▪ String: ▪ x = ‘A’ ▪ x = ‘abc’ ▪ x = ‘4’ ▪ x = ‘4.0’ ▪ x*2 ▪ x + ‘3’ ▪ type(x + ‘3’) ▪ x + 3  Variable Types ▪ Conversions: ▪ int(‘4’) ▪ int(4.5) ▪ float(‘4.2’) ▪ float(‘4’) ▪ str(4.2) ▪ ‘Area=’ + str(4.2)  Get Input from User h ‘5’ h=input(‘Enter height: ’); Memory location to store the input Message to the user Keyword to hold the program execution to get input from the keyboard Enter height: 5 Note: the default input is string data type  Get Input from User h 5 h=int(input(‘Enter height: ‘)) Returns (substitutes in its place) the string ‘5’ int(‘5’)=5 Enter height: 5 ? Write a Python statement to take the circle radius from the user and store it in ‘R’.  Display to Screen print(h) h 5 a 102 Keyword to display Memory location to the screen to display → 5 print(a) → 102  Display to Screen print('Height = ' + str(h)) h 5 → Height = 5 print('Height =', h) a 102 → Height = 5 Note regarding separating by a comma: ▪ No type conversion needed ▪ Automatically inserts space between the elements print('Height =', h, 'and area =', a) → Height = 5 and area = 102  Arithmetic Expressions Operations x 4 ** Exponentiation (5**2 is 25) *, /, // Multiplication, division, and floor division y 3.5 +, - Addition and subtraction z 2 Examples a 6.5 x=4; y=3.5; z=2 a = x + y - 5 / (3+z) b 8.5 b = a + x / 2 (semicolon can be used to separate multiple lines) Operations are executed only one at a time according to their precedence (priority). We will study it further in future lectures  How to write a software program? 1. Read the problem statement, and identify ▪ The input and its range ▪ The output ▪ The relationship between the input and the output (how to compute the output) [Comprehend or understood] 2. Write your thoughts as a sequence of steps. [Algorithm] 3. Convert these steps to Code. [Program] 4. Test your code and compare your program result against a human result. [Testing]  Calculate Area of a Rectangle (Problem → Algorithm) ▪ How a computer can solve this problem? ▪ I get the values of the height and the → Get height as h width from you and I store them in my → Get width as w memory. ▪ Then I multiply them in my brain and → Calculate area = h*w store the result in my memory ▪ And inform you about the resultant value. → Print area  Calculate Area of a Rectangle (Algorithm → Program) Get height as h h = int(input(‘Enter height: ’)) Get width as w w = int(input(‘Enter width: ’)) Calculate area = h*w area = h * w Print area print(area)  Calculate Area of a Rectangle (Program and Testing) h 5 h=int(input(‘Enter height: ’)) w 4 w=int(input(‘Enter width: ’)) area 20 area = h * w print(area) Enter height: 5 Enter width: 4 20  Calculate Area of a Circle (Algorithm, Program, Testing) import math 1. Get radius r r = int(input(‘Enter radius:’)) 2. Calculate area = pi*r**2 area = math.pi*r**2 3. Print area print(area) radius 5 area 78.5398 Enter radius: 5 78.5398  Calculate Number of Buses to Transfer Students (Algorithm) 1.Get number of students as numS 2.Get the bus capacity as busC 3.Calculate num of buses as numB = numS/busC (round up) 4. Print numB  Calculate Number of Buses to Transfer Students (Program) import math numS = int(input(‘Enter number of students:’)) busC = int(input(‘Enter bus capacity:’)) numB = numS/busC → numB = math.ceil(numS/busC) print(numB) If numS=60 and busC = 50 then numB = 60/50 = 1.2 ??? But it should be 2 math.ceil(1.2) = 2 ceil rounds up to nearest integer math.floor(1.2) = 1 floor rounds down to nearest integer  Calculate Number of Dozens and Remainder (Algorithm) 1.Get a number as N 2.Calculate dozen = N/12 (no fraction) 3.Calculate the remainder (r) of dividing N by 12 4.Print dozen 5.Print r  Calculate Number of Dozens and Remainder (Program) import math N = int(input(‘Enter a number’)) dozen = N/12 → dozen = N // 12 r = ?? →r = N % 12 print(dozen) print(r) N // 12 is the same as math.floor(N / 12) // called floor division