IndentationError: unexpected indent

Python IndentationError has a platform-specific cause particularly common on Windows: CRLF ( ) line endings mixed with LF ( ). Windows text editors and Git on Windows (without .gitattributes configuration) use line endings. Some editors introduce a mix of CRLF and LF within the same file during copy-paste operations, which the Python parser interprets as inconsistent indentation even when the code looks correct visually. Notepad++ shows line ending indicators; VS Code displays CRLF or LF in the bottom status bar. Converting to LF often resolves mysterious IndentationError instances. The command python -c "import tokenize; list(tokenize.open('file.py'))" exposes tokenization errors with the exact line and character position. A second Windows-specific cause: copy-pasting code from websites that use non-breaking spaces (Unicode U+00A0) instead of regular ASCII spaces. These look identical on screen but Python rejects them as invalid indentation characters. Open the file in a hex editor or run cat -A file.py (in WSL) to reveal hidden characters. VS Code's Show Whitespace setting exposes non-standard whitespace characters. The fix is to select all, remove all whitespace, and re-indent with consistent 4-space blocks using the editor's built-in re-indent function.