# IndentationError: unexpected indent / expected an indented block

**Code:** `IndentationError` · **Category:** Python · **Seen on:** Python

Python’s block structure is broken — inconsistent indentation or mixed tabs and spaces.

## Meaning

Indentation is syntax in Python. Every block after `:` must be indented consistently, and mixing tabs and spaces (TabError) is not allowed.

## Common causes

- Mixed tabs and spaces
- Empty block after `if`/`def`/`for` (use `pass`)
- Copy-pasted code with different indentation
- Stray indentation on a top-level line

## Quick fix

1. Configure the editor to insert 4 spaces
2. Convert tabs to spaces for the file
3. Add `pass` to empty blocks

## Detailed fix by platform

### Python

1. `python -m tabnanny file.py` reports ambiguous indentation.

## Code examples

### Empty block needs pass

```python
def todo():
    # ❌ IndentationError: expected an indented block
def todo():
    pass        # ✅
```

### Convert tabs to spaces

```bash
python -m tabnanny app.py           # reports ambiguous lines
expand -t 4 app.py > app_fixed.py   # tabs → 4 spaces
```

## How to diagnose

1. **Line** — Reported line and the block header above it
2. **Whitespace** — Show invisible characters in your editor — tabs vs spaces?
3. **Empty blocks** — Any if/def/for with no body?

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Source: [WhatIsMyError](https://whatismyerror.com/errors/python/indentationerror)