IndentationError: expected an indented block

What you see

def greet(name):
    if name:
    print("Hello,", name)

greet("Ada")

  File "/home/me/project/main.py", line 3
    print("Hello,", name)
    ^^^^^
IndentationError: expected an indented block after 'if' statement on line 2

What it means

A line that ends in a colon opens a block: if, elif, else, for, while, def, class, with, try, except, finally and match. The next line must be indented further than the line with the colon. Here print sits at the same depth as if, so the if has no body.

From Python 3.10 the message names the statement and the line it is on, which points straight at the block that is empty.

Why it happens

• The body was not indented, as in the example.
• A block was left empty on purpose, as a placeholder: def todo(): with nothing under it.
• The body is only a comment. Comments are ignored, so if ready: followed by # later is an if with no body.
• Pasted code lost its leading spaces, which happens with chat apps and some web pages.

How to fix it

Indent the body one level, four spaces by convention:

def greet(name):
    if name:
        print("Hello,", name)

For a block you mean to leave empty, write pass. ... also works:

def todo():
    pass

How each Python version words it

Run on CPython 3.9.6, 3.10.22, 3.11.17, 3.12.15, 3.13.17, 3.14.9 and 3.15.1, on October 25, 2026.

Up to 3.9 the message was only "expected an indented block". From 3.10 it adds what kind of block and its line number.