Fix Python reserved keyword 'class' in auto-generated Kaitai parser

[andrewmonostate]

The auto-generated Kaitai Struct parser polyfile/kaitai/parsers/openpgp_message.py contains invalid Python syntax. It uses self.class = ... which causes a SyntaxError because class is a reserved keyword in Python.

Error

File "polyfile/kaitai/parsers/openpgp_message.py", line 370
    self.class = self._io.read_u1()
         ^^^^^
SyntaxError: invalid syntax

Root Cause

The Kaitai Struct compiler generates Python code without escaping reserved keywords. This affects lines 361, 369, 370, and 371 in openpgp_message.py.

Upstream Fix Status

A fix has been submitted to the Kaitai Struct compiler upstream to address the root cause:

• PR: kaitai-io/kaitai_struct_compiler#320

Solution

This PR provides an interim fix that:

1. Automatically patches the issue on import - The fix is applied transparently when polyfile is imported
2. Includes a manual fix script (fix_class_keyword.py) for development/debugging
3. Updates documentation with a Known Issues section

The fix replaces all occurrences of self.class with self.class_ (following PEP 8 conventions).

Changes

• polyfile/__init__.py: Added _fix_class_keyword_if_needed() auto-fix function
• polyfile/kaitai/parsers/openpgp_message.py: Auto-fixed by the import hook
• fix_class_keyword.py: Standalone script for manual fixing if needed
• README.md: Added Known Issues section documenting the problem and fix
• .gitignore: Added *.egg-info/ to ignore build artifacts

Testing

The fix successfully:

• Replaces self.class with self.class_ (line 370)
• Updates SEQ_FIELDS from "class" to "class_" (line 361)
• Updates debug references from ['class'] to ['class_'] (lines 369, 371)
• Allows polyfile to be imported without errors

Note

Once the upstream fix in the Kaitai Struct compiler is merged and new parsers are generated, this workaround will no longer be necessary.

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