The yapf.sh script checks for specific "known-to-work-with-YAPF" versions of Python to run YAPF with. On my machine, I have python3.11 and python3.12 (python3 is a symlink to python3.12). However, the python3.11 release doesn't have lib2to3 so the YAPF script fails with:

Checking Python formatting...
To fix, run `et format` or:                                                                                   

git apply <<DONE
  /usr/local/google/home/het/Projects/flutter/engine/src/flutter/tools/gn
Traceback (most recent call last):
  File "<frozen runpy>", line 198, in _run_module_as_main
  File "<frozen runpy>", line 88, in _run_code
  File "/usr/local/google/home/het/Projects/flutter/engine/src/flutter/third_party/yapf/yapf/__main__.py", line 16, in <module>
    import yapf
  File "/usr/local/google/home/het/Projects/flutter/engine/src/flutter/third_party/yapf/yapf/__init__.py", line 35, in <module>
    from yapf.yapflib import errors
  File "/usr/local/google/home/het/Projects/flutter/engine/src/flutter/third_party/yapf/yapf/yapflib/errors.py", line 16, in <module>
    from lib2to3.pgen2 import tokenize
ModuleNotFoundError: No module named 'lib2to3'

DONE

On my Ubuntu machine I cannot install lib2to3 through normal APT packages; apt install python3.11-lib2to3 fails since that package has been obsoleted. I've been able to work around this by manually editing the yapf.sh script to not check for python3.10 or python3.11 first.

See #158384

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