In Python, programs are executed sequentially; the Python interpreter reads a program one line at a time, from left to right and top to bottom, just as you read this page. The interpreter executes operations and functions in the order that they appear. This is known as control flow.

Without control flow expressions, a program is simply a collection of statements that are executed sequentially. Control flow allows you to execute specific code blocks conditionally and/or repeatedly, and these fundamental building blocks can be combined to create complex code.

In our previous blog, we explored the building blocks of Python programs: variables and data types. Now, we’re venturing into the realm of control flow, a fundamental concept that empowers your programs to make decisions, repeat actions, and structure their logic effectively. Just like variables and data types provide the foundation for storing and manipulating information, control flow mechanisms dictate how your program executes, transforming it from a static collection of instructions into a dynamic and interactive entity.

This blog post will serve as your comprehensive guide to control flow in Python, equipping you with the tools to craft powerful and versatile programs. So, buckle up and get ready to unlock the true potential of your Python code!

Conditional Statements

Conditional statements enable your code to make decisions based on specific conditions. The main conditional statements in Python are if, elif, and else.

If Statements:

The if statement is one of the most common control flow statement types. It checks a condition and then performs one of two functions:

Let’s say we want to know whether the input value of an is positive or negative. We use the if statement to specify two conditions: if an is greater than 0, print ‘Its positive’; if an is less than 0, print ‘Its negative.’

If the set condition is True, the code in the next block is executed.
If the set condition is False, the code in the next block is ignored.

The code snippet highlights this code behavior:

a = 0
if a > 0:
    print("Positive")

Output:
Positive

if  a < 0:
    print("Negative")
    
Output: #Observer that print was not executed because condition didn’t evaluate to true.

elif and else:

An if statement can be followed by one or more elif blocks, as well as a catch-all else block, if all of the conditions are false.

The code snippet highlights the code behavior using the elif and else code blocks.

Example:

def check_no(x):
    if x<0:
        print("Its Negative")
    elif x==0:
        print("Equal to Zero")
    elif 0<x<5:
        print("Positive but smaller than 5")
    else:
        print("Positive and larger than or equal to 5")
        
check_no(-10)

Output:
Its Negative

Now try with check_no(10)

Output:
Positive and larger than or equal to 5

Now Try with 0 check_no(0)

Output:
Equal to Zero

Now Try with check_no(4)

Output: Positive but smaller than 5

Python Loops:

Loops allow you to execute a block of code repeatedly. Python has two main types of loops: for and while.

For Loops:

for loop iterates over a sequence (like a list, tuple, dictionary, or string) and executes a block of code for each item in the sequence.

fruits = ["apple", "banana", "cherry"]
for fruit in fruits:
    print(fruit)

The for loop iterates over each item in the fruits list and prints it. The output will be:

While Loop

A while loop executes as long as a specified condition is true.

count = 1
while count <= 5:
    print(count)
    count += 1

The while loop runs as long as count is less than or equal to 5. It prints the current value of count and then increments it by 1. The output will be:

Conclusion

Mastering control flow is a cornerstone of becoming proficient in Python. By understanding and effectively using conditional statements, loops, and comprehensions, you can write more efficient and readable code. Experiment with these concepts in your projects to see how they can simplify complex tasks.

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