Python Program Execution

In this tutorial, we will walk through step by step explanation about execution of a python program.

Program execution

Python Program can be executed in a three ways, lets write a sample program to find sum of two numbers Python and explore the execution process steps involved.

a = 10
b = 20
print("The Sum : ",(a+b))						
						

By observing the code of same program in different programming language we can easily decide that Python code will be simple and concise.

Execution of Python Program :

Compare program execution with Java and C :

Execution of C Program

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Execution of Java Program

Ways of Python Program Execution

There are three ways of executing a Python program

1. Using Python's command line window
2. Using Python's IDLE graphics window
3. Directly from System prompt

The first two are called interactive modes where we can type the program one line at a time and the PVM executes it immediately. The last one is called non-interactive mode where we ask the PVM to execute our program after typing the entire program

Comments in Python

There are two types of comments in Python

1. Single line comments
2. Multi line comments

Single line comments

These comments start with a hash symbol (#) and are useful to mention that the entire line till the end should be treated as comment

For example

#To find sum of two numbers 
a = 10 #store 10 into variable a 

Here, the first line is starting with a #and hence the entire line is treated as a comment. In the second line, a = 10 is a statement. After this statement, #symbol starts the comment describing that the value 10 is stored into variable 'a'. The part of this line starting from #symbol to the end is treated as a comment.

Comments are non-executable statements. It means neither the Python compiler nor the PVM will execute them. Comments are for the purpose of understanding human beings and not for the compiler or PVM. Hence, they are called non-executable statements

Multi line comments

When we want to mark several lines as comment, then writing #symbol in the beginning of every line will be a tedious job.

For example

#This is a program to find net salary of an employee 
#based on the basic salary, provident fund, house rent allowance, 
#dearness allowance and income tax. 

Instead of starting every line with #symbol, we can write the previous block of code inside """ (triple double quotes) or ''' (triple single quotes) in the beginning and ending of the block as:

""" This is a program to find net salary of an employee based 
on the basic salary, provident fund, house rent allowance, 
dearness allowance and income tax. """ 

Or

''' This is a program to find net salary of an employee based 
on the basic salary, provident fund, house rent allowance, 
dearness allowance and income tax. '''

The triple double quotes (""") or triple single quotes (''') are called 'multi line comments' or 'block comments'. They are used to enclose a block of lines as comments.