IndentationError

Q: What does "unindent does not match any outer indentation level" mean?

A line was dedented to a column that no enclosing block uses — for example a block at 8 spaces followed by a line at 2 spaces when the outer levels are 0 and 4. Dedent exactly to one of the enclosing levels. Invisible tabs are a common cause; turn on whitespace rendering in your editor.

Q: What is TabError and how do I fix it?

TabError (a subclass of IndentationError) is raised when tabs and spaces are mixed so that whether two lines line up depends on the tab width. Python checks indentation twice — tabs as 8 columns and tabs as 1 column — and both must agree. Fix it by converting the file to spaces (most editors have "convert indentation to spaces", or use str.expandtabs).

Q: Why do I get "unexpected indent" in exec() or the REPL?

The first statement of a string passed to exec()/compile() must start at column 0. Code copied from inside a function or a triple-quoted string keeps its leading spaces; remove them with textwrap.dedent().

Q: Is IndentationError a SyntaxError?

Yes: TabError → IndentationError → SyntaxError → Exception. It is detected while compiling, so it has the same msg, filename, lineno, offset and text attributes and the same rule: a try/except in the same file cannot catch it.

In Python the indentation is the block structure, so a wrong indent is a syntax error — raised at compile time, with TabError as the special case for tabs and spaces that only line up at some tab widths.

InheritsBaseException›Exception›SyntaxError›IndentationError

Import / syntax exceptionPython 3 (all)Live demo

IndentationError(messagemessage — The error text (e.msg).type: str · default: null, detailsdetails — Same as SyntaxError: (filename, lineno, offset, text[, end_lineno, end_offset]).type: tuple · default: null)

Raised by

compiling a file, exec(), compile() — never while code runs

Message

expected an indented block after … · unexpected indent · unindent does not match any outer indentation level

Quick fix

indent with 4 spaces everywhere; an empty body needs pass

Watch out

TabError: a tab and 8 spaces look identical but are rejected

Demo

Live evaluation

A three-line loop. Choose how many spaces indent line 2 and line 3 — the numbers decide whether line 3 is inside the loop, after it, or an error.

Try:

Inputs

firstintspaces before line 2

secondintspaces before line 3

Code

src = 'for i in range(3):\n' + ' ' * 4 + 'n += 1\n' + ' ' * 4 + 'n += 10\n'
n = 0
exec(src)
n

Result

In Trigger, 4 / 4 gives 33 (line 3 runs three times inside the loop) and 4 / 0 gives 13 (once, after it) — same code, different meaning. 4 / 2 dedents to a column no enclosing block uses. In Handle, a tab and 8 spaces reach the same column, yet Python raises TabError: it also measures every line with a tab counted as 1 column, and the two measurements must agree about which lines line up.

Constructor

Name	Type	Required	Description
message	str	no	The error text (e.msg).
details	tuple	no	Same as SyntaxError: (filename, lineno, offset, text[, end_lineno, end_offset]).

Attributes

Attribute	Type	Meaning
msg	str	The message, e.g. "expected an indented block after 'if' statement on line 1" — note it names the statement and line that needed the block.
lineno	int \| None	The line with the bad indentation (for a missing block, the line that should have been indented).
text	str \| None	That source line.
offset / filename / end_lineno / end_offset	int \| str \| None	Inherited from SyntaxError.

Common patterns

An empty block needs a statement

pass, ... or a docstring all count as a body. A comment does not.

def not_ready_yet():
    pass

class Placeholder:
    """Filled in later."""

Dedent code stored in strings

Source kept in an indented triple-quoted string starts with spaces — dedent it before compile()/exec().

import textwrap
snippet = '''
    def f():
        return 1
'''
exec(textwrap.dedent(snippet))

Normalize tabs in legacy files

Convert tabs to spaces once (editor "convert indentation", or expandtabs), then keep a single style.

with open('legacy.py', encoding='utf-8') as f:
    fixed = f.read().expandtabs(4)

Examples

1. Block without a body

src = 'if ok:\nreturn 1' try: compile(src, 'app.py', 'exec') except IndentationError as e: r = (e.msg, e.lineno, e.text) r

Returns

("expected an indented block after 'if' statement on line 1", 2, 'return 1\n')

2. One space too many

src = 'def f():\n x = 1\n return x' compile(src, 'app.py', 'exec')

Returns

IndentationError: unexpected indent

3. Dedent to a level that never existed

src = 'def f():\n if x:\n pass\n return x' compile(src, 'app.py', 'exec')

Returns

IndentationError: unindent does not match any outer indentation level

4. TabError: 4 spaces then a tab

src = 'def f():\n x = 1\n\treturn x' compile(src, 'app.py', 'exec')

Returns

TabError: inconsistent use of tabs and spaces in indentation

5. Tabs only are fine

src = 'def f():\n\tx = 1\n\treturn x' compile(src, 'app.py', 'exec') is not None

Returns

True

6. TabError is an IndentationError is a SyntaxError

try: compile('if x:\n a = 1\n\tb = 2', 'app.py', 'exec') except SyntaxError as e: r = type(e).__mro__[:3] [c.__name__ for c in r]

Returns

['TabError', 'IndentationError', 'SyntaxError']

7. Leading spaces in exec()

exec(' x = 1')

Returns

IndentationError: unexpected indent

Pitfalls

1. A comment is not a block body

Comments are dropped by the tokenizer, so a block containing only a comment is empty.

Comment only

src = 'def todo():\n    # later\n'
compile(src, 'app.py', 'exec')

IndentationError: expected an indented block after function definition on line 1

Add pass

src = 'def todo():\n    # later\n    pass\n'
compile(src, 'app.py', 'exec') is not None

True

2. Indented code in a triple-quoted string

The string keeps the indentation of the surrounding source, so its first statement is "unexpectedly" indented.

As written

code = '''
    def f():
        return 1
'''
compile(code, 'app.py', 'exec')

IndentationError: unexpected indent

textwrap.dedent

import textwrap
code = '''
    def f():
        return 1
'''
compile(textwrap.dedent(code), 'app.py', 'exec') is not None

True

3. Pasted code that mixes tabs and spaces

Lines that look aligned in the editor can be a tab on one line and spaces on the next. Convert the file to spaces instead of adjusting single lines.

Mixed

src = 'def f():\n    x = 1\n\treturn x'
compile(src, 'app.py', 'exec')

TabError: inconsistent use of tabs and spaces in indentation

expandtabs(4)

src = 'def f():\n    x = 1\n\treturn x'
compile(src.expandtabs(4), 'app.py', 'exec') is not None

True

When to use

Use it

Catching it (or SyntaxError) around compile()/exec() of generated or user-supplied code
Raising it from a tool that parses an indentation-based format

Reach for something else

Catching it in your own module → it is compiled before any try runs; fix the file
Fixing TabError line by line → convert the whole file to spaces

Notes

CPython impl

Parser/lexer/lexer.c — each line gets col (tab = next multiple of 8) and altcol (tab = 1); if the two disagree about indent/dedent/same level, TabError. "unexpected indent" and "expected an indented block" come from the parser

Catch via

except SyntaxError catches IndentationError and TabError

TabError

Subclass of IndentationError: "inconsistent use of tabs and spaces in indentation"

PEP8

4 spaces per level; never mix tabs and spaces

FAQ

How do I fix "IndentationError: expected an indented block"? ▾

The line after a statement ending in a colon (if, for, while, def, class, with, try, except, match …) must be indented deeper. The message names that statement and its line number. If the block is intentionally empty, write pass (or ...) — a comment alone is not a body.

What does "unindent does not match any outer indentation level" mean? ▾

What is TabError and how do I fix it? ▾

Why do I get "unexpected indent" in exec() or the REPL? ▾

Is IndentationError a SyntaxError? ▾

IndentationError

Demo

Constructor

Attributes

Common patterns

Examples

Pitfalls

When to use

Notes

Related

FAQ