Fix 'IndentationError: expected an indented block' in Python

TL;DR

You wrote a colon (:) but left the block below it empty. Python can't proceed without at least one statement there. Either add the actual code, or drop in a pass as a placeholder. Also check that you're not mixing tabs and spaces — Python 3 treats that as a hard error.

What Triggers This Error

In Python, a colon isn't just punctuation — it's a promise. Every statement ending with : must be followed by an indented block. This applies to if, else, elif, for, while, def, class, with, and try/except/finally.

Skip the body, and Python throws:

IndentationError: expected an indented block

Common Scenarios and Fixes

1. Empty function or class body

You stub out a function or class but haven't written the body yet:

# Bad
def my_function():

class MyClass:

Fix — add pass:

# Good
def my_function():
    pass

class MyClass:
    pass

2. Comment-only body

Comments don't count as statements. Python still sees an empty block — that # TODO might as well not be there:

# Bad
def process():
    # TODO: implement this

def main():
    # coming soon

Fix — pair the comment with pass:

# Good
def process():
    # TODO: implement this
    pass

3. if/else with missing body

# Bad
if condition:
else:
    do_something()

Fix:

# Good
if condition:
    pass
else:
    do_something()

4. try/except with empty block

# Bad
try:
except ValueError:
    handle_error()

Fix:

# Good
try:
    risky_call()
except ValueError:
    handle_error()

5. Mixed tabs and spaces

This one's easy to miss. The code looks indented in your editor, but one line uses a tab while another uses spaces. Python 3 rejects this outright. You might see a TabError, but it sometimes surfaces as an IndentationError instead.

# Bad (tab on one line, spaces on another)
def greet():
	print("hello")   # tab
    print("world")   # spaces

Standardize to spaces — 4 per level, as PEP 8 recommends:

def greet():
    print("hello")
    print("world")

To bulk-convert in your editor: VS Code → Command Palette → "Convert Indentation to Spaces". In vim, run :retab. From the terminal:

expand -t 4 myfile.py > myfile_fixed.py

6. Accidentally un-indented block

# Bad
for item in items:
print(item)   # not indented

Fix:

# Good
for item in items:
    print(item)

Reading the Traceback

Python's error message points straight at the problem:

  File "script.py", line 5
    def helper():
              ^
IndentationError: expected an indented block

Line 5 is where Python expected a body to begin. Look at the line before the caret — that's your colon. The block below it is empty or indented wrong.

Quick Checklist

• Every : at the end of a line must be followed by an indented block on the next line.
• Empty blocks need pass.
• A comment alone doesn't satisfy the block requirement — add pass below it.
• Use spaces only — 4 per level. Set your editor to insert spaces when you press Tab.
• Run python -m py_compile yourfile.py to catch syntax errors before executing.

Verifying the Fix

Run a quick syntax check without executing the file:

python -m py_compile script.py
echo $?   # 0 means clean

For broader style and error checking, flake8 covers more ground:

pip install flake8
flake8 script.py

No output, no problems. If py_compile exits with 0, the IndentationError is gone.

Editor Settings to Prevent This

• VS Code: set "editor.tabSize": 4 and "editor.insertSpaces": true in settings.json.
• PyCharm: already defaults to 4-space indentation for Python files.
• Vim: add autocmd FileType python setlocal expandtab shiftwidth=4 tabstop=4 to .vimrc.