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Indentation

Python Basics

In one line

Indentation is the leading whitespace before a line of code. In Python, it defines code blocks instead of braces.

In simple words

In Python, indentation is not just for readability — it is syntactically significant. The number of spaces at the start of a line determines which block of code the line belongs to. This is how Python groups statements, instead of using curly braces like JavaScript or C.

Consistent indentation is mandatory. Mixing tabs and spaces causes errors. The convention is four spaces per level (PEP 8). A line inside an if, for, or def must be indented one level deeper than the statement that introduces the block.

Indentation makes Python code visually clean and forces a consistent style. The downside is that a single misplaced space can change the meaning of your code or cause an IndentationError. Most editors handle this automatically, but it is important to understand.

Example

python
age = 20

if age >= 18:
    print("Adult")      # indented — inside the if
    print("Can vote")   # indented — inside the if
print("Done")           # not indented — outside the if

# Wrong indentation causes an error:
# if age >= 18:
# print("Adult")  # IndentationError: expected an indented block

Lines indented under if belong to the if-block. The unindented line runs regardless. Wrong indentation is a syntax error.

Common confusions

  • Confused with: braces

    The difference: Python uses indentation to define code blocks; most other languages (JavaScript, Java, C) use curly braces {}. Indentation is mandatory and semantic in Python, while braces are mandatory and indentation is optional (style only) in those languages.

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