Python reserved keyword 'class' blocking Weave installation

[andrewmonostate]

This bug prevents the installation and usage of Weights & Biases Weave in python 3.9 where compiling happens at install because polyfile-weave is a dependency of Weave. When Weave tries to import polyfile, it fails with a SyntaxError, making Weave completely unusable.

How This Was Discovered

While trying to use Weave for ML experiment tracking, we encountered:

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

This import error cascades up and prevents Weave from functioning.

The Problem

The Kaitai Struct compiler generates invalid Python code in polyfile/kaitai/parsers/openpgp_message.py. It uses self.class = ... which causes a SyntaxError because class is a reserved keyword in Python (since Python 1.0).

Impact

• Blocks Weave installation/usage - Critical for ML practitioners using W&B
• Affects any Python project depending on polyfile-weave
• Prevents parsing of OpenPGP messages

Solution

This PR adds automatic patching that fixes the issue transparently on import, ensuring both polyfile-weave and its dependents (like Weave) work out-of-the-box.

Changes Made

1. polyfile/__init__.py: Added _fix_class_keyword_if_needed() function that:

   • Detects if openpgp_message.py uses the reserved keyword class
   • Automatically replaces self.class with self.class_ before module imports
   • Runs silently without breaking imports if any issues occur
   • Ensures Weave can successfully import polyfile

2. polyfile/kaitai/parsers/openpgp_message.py: Auto-fixed by the import hook:

   • Line 370: self.class → self.class_
   • Line 361: SEQ_FIELDS = ["class"...] → SEQ_FIELDS = ["class_"...]
   • Lines 369, 371: ['class'] → ['class_']

3. fix_class_keyword.py: Standalone script for manual fixing if needed

4. README.md: Updated with Known Issues section

5. .gitignore: Added *.egg-info/ to ignore build artifacts

Testing

The fix has been tested and successfully:

• Allows Weave to be imported and used normally
• Allows polyfile-weave to be imported without errors
• Preserves all functionality
• Works with all Python versions (3.9 through 3.13 tested)

Verification

# Before fix:
>>> import weave  # SyntaxError!

# After fix:
>>> import weave  # ✅ Works!
>>> weave.init("my-project")  # ✅ Works!

Related Fixes

• Upstream (Kaitai Compiler): PR submitted to fix at the source - [Fix Python reserved keyword escaping in code generation kaitai-io/kaitai_struct_compiler#320]
• Original polyfile: Similar fix submitted to trailofbits/polyfile

Note

This is a workaround for a bug in the Kaitai Struct compiler. Once the compiler is fixed upstream and new parsers are generated, this auto-fix will no longer be necessary but will remain harmless if left in place.

[zbirenbaum]

Thanks for this! sorry I seem to have missed the notification