Indentation in Python

Indentation is the use of spaces or tabs at the beginning of a line to define the structure and grouping of code. In Python, indentation is not just for readability—it is a part of the syntax itself.

Unlike many programming languages that use braces {} or keywords to mark blocks of code (like loops, functions, conditionals), Python uses indentation levels to group statements. This means that the amount of leading whitespace matters a lot.

Why is indentation important?

• It shows which statements belong together.
• It determines the scope or block of code (for example, what code runs inside an if statement or a for loop).
• Incorrect indentation causes syntax errors.

Example of indentation in Python

if 5 > 2:
    print("Five is greater than two!")
    print("This line is also inside the if block")
print("This line is outside the if block")

Output:

Five is greater than two!
This line is also inside the if block
This line is outside the if block

• The two print statements that are indented belong to the if block.
• The last print statement is outside the if block because it’s not indented.

Incorrect indentation example — causes error

if 5 > 2:
print("This will cause an IndentationError")

Error:

IndentationError: expected an indented block

Indentation with loops

for i in range(3):
    print(f"Iteration {i}")
    print("Inside the loop")

print("Outside the loop")

Output:

Iteration 0
Inside the loop
Iteration 1
Inside the loop
Iteration 2
Inside the loop
Outside the loop

Mixing tabs and spaces

• Always use either spaces or tabs consistently (PEP 8 recommends 4 spaces per indentation level).
• Mixing tabs and spaces can cause errors or unpredictable behavior.

Summary:

• Indentation is mandatory in Python to define code blocks.
• Typical indentation is 4 spaces.
• Incorrect or inconsistent indentation raises IndentationError.
• Indentation improves code readability and structure.