Slides for Lecture 1 of the course: Introduction to Programming with Python offered at ICCBS. It covers the following topics: 1.) Variables, Statements and Expressions 2.) Functions 3.) Flow Control

1. Introduction to
Programming with
Python – Class 1
SYED FARJAD ZIA ZAIDI

2. Class Objectives
Class Objective
Review variables, statements, expressions, functions, algorithms and technical
terms.
Understanding Flow Control.
Write a simple program that performs addition, subtraction, multiplication and
division using Functions.

3. Class Material
•Chapter 1, 2, 3 - Python
for Informatics: Exploring
Information
Reading
Assignment •Rock, Paper, Scissors

4. Variables
 Definition:
A named piece of memory that can store a value.
 Statement:
A statement written in a programming language stores a value in a variable.
Example:
X = 5
Y = 1
 Expression:
A variable that has a value can be used in an expression.
Example:
X = X + 4
Y = X + 1

5. Rules for defining a Variable:
 Names must start with a letter or _.
 Names must contain only letters, digits, and _.

6. Questions?

7. Functions
 Definition:
A function is a block of organized, reusable code that is used to perform
some action.
 Defining a function:
You can define a function in Python using the Keyword ‘def’.
 General Form of Function:
def function_name(parameters):
body
Example:
def MyFirstFunction():
print “This is my first function in Python Programming Language”

8. Defining Functions
You can define functions to provide the required functionality. Here
are simple rules to define a function in Python.
 Function blocks begin with the keyword ‘def’ followed by the
function name and parentheses ‘( )’ .
Example:
def MyFirstFunction():
 Any input parameters or arguments should be placed within these
parentheses. You can also define parameters inside these
parentheses.
Example:
def MySecondFunction(passedInput):

9. Defining Functions
 The first statement of a function can be an optional statement - the
documentation string of the function or docstring.
Example:
def MyFirstFunction():
“””This is the 'docstring' which defines
the function for other programmers to
understand easily”””
 The code block within every function starts with a colon (:) and is
indented.

10. Defining Functions
 The statement return [expression] exits a function, optionally passing
back an expression to the caller. A return statement with no
arguments is the same as return None.
 General Form of Return Statement:
return [expression]
Example:
def MyFunction():
“”“A function that returns a message”””
return “This is a function that returns a message”

11. Calling a function
 Function calls are expressions and the result can be stored in a
variable. The general form of a function call:
function_name(arguments)
Example:
MyFirstFunction()
MySecondFunction(“Input Parameter”)

12. Questions?

13. Source Code vs Object Code
Source Code Object Code
Source Code is a text file version of
a computer program or software that
contains instructions that the
computer follows to do something
Object code, or sometimes an object
module, is what a
computer compiler produces
Source code is written in
a programming language which a
human can read and change
In a general sense object code is a
sequence of statements or instructions
in a computer language, usually
a machine code language (i.e., 1's
and 0's)
Most source code is compiled when it
is finished
Object code is the resulting code
after compiling source code

14. Compiler
 A compiler is a computer program (or set of programs) that
transforms source code written in a programming language (the
source language) into another computer language (the target
language, often having a binary form known as object code). The
most common reason for wanting to transform source code is to
create an executable program.

15. Questions?

16. Flow Control of the Program
 Selection (If/Else)
 Repetition (Loops)

17. Conditional Execution
 In order to write useful programs, we almost always need to check
some conditions and change the program accordingly. Conditional
Statements gives us this ability. The simplest form is if statement.
 General Form:
if [expression1]:
body1
elif [expression2]:
body2
else:
bodyN

18. Python Comparison Operators
Operator Description
== Checks if the value of two operands are equal or not, if yes
then condition becomes true.
!= Checks if the value of two operands are equal or not, if
values are not equal then condition becomes true.
< Checks if the value of left operand is less than the value of right
operand, if yes then condition becomes true.
> Checks if the value of left operand is greater than the value of right
operand, if yes then condition becomes true.
>= Checks if the value of left operand is greater than or equal
to the value of right operand, if yes then condition becomes
true.
<= Checks if the value of left operand is less than or equal to
the value of right operand, if yes then condition becomes
true.

19. Python Logical Operators
Operator Description
and Called Logical AND operator. If both the operands are
true then then condition becomes true.
or Called Logical OR Operator. If any of the two operands
are non zero then then condition becomes true.
not Called Logical NOT Operator. Use to reverses the logical
state of its operand. If a condition is true then Logical NOT
operator will make false.

20. Questions?

21. Simple Calculator
 Definition:
A calculator is a machine which allows people to do math operations
more easily. For example, most calculators will add, subtract, multiply, and
divide.
 Instructions for writing the Program:
 There should be 4 functions in your program:
 Add(number1, number2)
 Subtract(number1, number2)
 Multiply(number1, number2)
 Divide(number1, number2)
 The template for the program can be accessed here:
http://www.codeskulptor.org/#user37_44o34rWsnC_18.py

22. Questions?

23. Rock Paper Scissors – 1st Mini-
Project
Rock-paper-scissors is a hand game that is played by two people. The
players count to three in unison and simultaneously "throw” one of
three hand signals that correspond to rock, paper or scissors. The
winner is determined by the rules:
 Rock smashes scissors
 Scissors cuts paper
 Paper covers rock

24. Instruction
 In our first mini-project, we will build a Python function rps(name)
that takes as input the string name, which is one of "rock", "paper",
"scissors“. The function then simulates playing a round of rock-paper-scissors
by calling a helper function gen_random_num() that
generate own random choice from these alternatives and then
determining the winner using simple if / else statements.
 The mini-project template is here:
http://www.codeskulptor.org/#user37_HJPdXx35jy_0.py

25. Example runs
Player chooses rock
Computer chooses scissors
Player wins!
Player chooses paper
Computer chooses scissors
Computer wins!
Player chooses scissors
Computer chooses paper
Player wins!

26. Questions?