Weird import conflict with xarray and typing-extensions on Python 3.8

[soxofaan]

One of our CI builds suddenly started failing with this stack trace:

tests/util/test_logging.py:1: in <module>
    import dirty_equals
venv38/lib64/python3.8/site-packages/dirty_equals/__init__.py:38: in <module>
    from ._sequence import Contains, HasLen, IsList, IsListOrTuple, IsTuple
venv38/lib64/python3.8/site-packages/dirty_equals/_sequence.py:215: in <module>
    class IsList(IsListOrTuple[List[Any]]):
/usr/lib64/python3.8/typing.py:258: in inner
    return cached(*args, **kwds)
/usr/lib64/python3.8/typing.py:895: in __class_getitem__
    return _GenericAlias(cls, params)
/usr/lib64/python3.8/typing.py:669: in __init__
    self.__parameters__ = _collect_type_vars(params)
venv38/lib64/python3.8/site-packages/typing_extensions.py:2994: in _collect_type_vars
    enforce_default_ordering = _has_generic_or_protocol_as_origin()
venv38/lib64/python3.8/site-packages/typing_extensions.py:2961: in _has_generic_or_protocol_as_origin
    return frame.f_locals.get("origin") in (
venv38/lib64/python3.8/site-packages/dirty_equals/_base.py:20: in __eq__
    return self() == other
venv38/lib64/python3.8/site-packages/dirty_equals/_sequence.py:181: in __init__
    length=_length_repr(self.length),
E   NameError: name '_length_repr' is not defined

After some rabbit hole crawling I could zoom in on a minimal reproduction procedure.
The problem started with the release of typing-extensions 4.12.1 (June 1st, 2024) and happens when xarray is imported before dirty_equals.

Example in a fresh docker run --rm -it python:3.8 /bin/bash container:

root@0a0f1606b929:/# pip install xarray dirty-equals typing-extensions
...
Successfully installed dirty-equals-0.7.1.post0 numpy-1.24.4 packaging-24.0 pandas-2.0.3 python-dateutil-2.9.0.post0 pytz-2024.1 six-1.16.0 typing-extensions-4.12.1 tzdata-2024.1 xarray-2023.1.0
...

root@0a0f1606b929:/# python
>>> import xarray
>>> import dirty_equals
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/local/lib/python3.8/site-packages/dirty_equals/__init__.py", line 38, in <module>
    from ._sequence import Contains, HasLen, IsList, IsListOrTuple, IsTuple
  File "/usr/local/lib/python3.8/site-packages/dirty_equals/_sequence.py", line 215, in <module>
    class IsList(IsListOrTuple[List[Any]]):
  File "/usr/local/lib/python3.8/typing.py", line 258, in inner
    return cached(*args, **kwds)
  File "/usr/local/lib/python3.8/typing.py", line 898, in __class_getitem__
    return _GenericAlias(cls, params)
  File "/usr/local/lib/python3.8/typing.py", line 672, in __init__
    self.__parameters__ = _collect_type_vars(params)
  File "/usr/local/lib/python3.8/site-packages/typing_extensions.py", line 2994, in _collect_type_vars
    enforce_default_ordering = _has_generic_or_protocol_as_origin()
  File "/usr/local/lib/python3.8/site-packages/typing_extensions.py", line 2961, in _has_generic_or_protocol_as_origin
    return frame.f_locals.get("origin") in (
  File "/usr/local/lib/python3.8/site-packages/dirty_equals/_base.py", line 20, in __eq__
    return self() == other
  File "/usr/local/lib/python3.8/site-packages/dirty_equals/_sequence.py", line 181, in __init__
    length=_length_repr(self.length),
NameError: name '_length_repr' is not defined

Possible workarounds:

• pin down typing-extensions<4.12.1
• use python 3.9 or higher
• import dirty_equals before xarray

[soxofaan]

To give a bit more info about how the NameError occurs from current https://github.com/samuelcolvin/dirty-equals/blob/2c85486b29492977f82c850eadf1afc0e2a9434e/dirty_equals/_sequence.py:

IsListOrTuple.__init__ at line 87 calls _length_repr which is defined at line 257. Nothing out of the ordrinary.

But this line 215 in between:

dirty-equals/dirty_equals/_sequence.py

Line 215 in 2c85486

class IsList(IsListOrTuple[List[Any]]):

seems to trigger an instantiation of IsListOrTuple on Python 3.8 when xarray is already imported and typing-extensions 4.12.1 is installed. The instantiation doesn't work as _length_repr isn't defined yet causing the NameError

[soxofaan]

This might actually just be a bug/regression in typing-extensions as noted in python/typing_extensions#425

[soxofaan]

This issue seems to be resolved with recent typing-extensions 4.12.2 release.