IndentationError

A Python program uses indentation to nest blocks. Each statement in a block must have the same indentation level. But separate blocks may use different indents.

An IndentationError occurs if this rule is broken. Like the SyntaxError, the program can never be run and there is no way to force the program to run.

Example

This program causes an IndentationError (unexpected indent). In the for-loop, 2 print method calls appear. But the second print() call is indented further to the right than the first.

# An incorrectly-formatted for-loop.
for n in range(0, 1):
    print(n)
        print(n)
    print(n)
    ^
IndentationError: unexpected indent

Next, we find that indent levels have no requirement to be even throughout a program. In this example, the print-statements are unevenly-indented.

# Correct.
for n in range(0, 1):
    print(n)

# Correct but different.
for n in range(0, 1):
        print(n)
0
0

Summary

Indentation is key in Python—it tells us how blocks are organized. Scope, a related concept, is also determined by indentation. The Python language requires strict indentation.