#21985·mypy

mypy RecursionError analyzing pint.facets.plain.quantity.PlainQuantity

Author: quentinCreated Sep 15, 2026Updated Sep 18, 2026

Labelscrashtopic-recursive-types

Crash Report

mypy crashes with RecursionError while analyzing pint (since pint==0.26.1). Reproduced with compiled and non-compiled mypy.

Traceback

python-traceback

... skipping approx 50000 lines ...
  File "/home/quentin/dev/QSA/pint_0.x/.venv/lib/python3.13/site-packages/mypy/type_visitor.py", line 560, in visit_instance
    return self.query_types(t.args)
           ~~~~~~~~~~~~~~~~^^^^^^^^
  File "/home/quentin/dev/QSA/pint_0.x/.venv/lib/python3.13/site-packages/mypy/type_visitor.py", line 628, in query_types
    return any(t.accept(self) for t in types)
  File "/home/quentin/dev/QSA/pint_0.x/.venv/lib/python3.13/site-packages/mypy/type_visitor.py", line 628, in <genexpr>
    return any(t.accept(self) for t in types)
               ~~~~~~~~^^^^^^
  File "/home/quentin/dev/QSA/pint_0.x/.venv/lib/python3.13/site-packages/mypy/types.py", line 1684, in accept
    return visitor.visit_instance(self)
           ~~~~~~~~~~~~~~~~~~~~~~^^^^^^
  File "/home/quentin/dev/QSA/pint_0.x/.venv/lib/python3.13/site-packages/mypy/type_visitor.py", line 560, in visit_instance
    return self.query_types(t.args)
           ~~~~~~~~~~~~~~~~^^^^^^^^
  File "/home/quentin/dev/QSA/pint_0.x/.venv/lib/python3.13/site-packages/mypy/type_visitor.py", line 628, in query_types
    return any(t.accept(self) for t in types)
  File "/home/quentin/dev/QSA/pint_0.x/.venv/lib/python3.13/site-packages/mypy/type_visitor.py", line 628, in <genexpr>
    return any(t.accept(self) for t in types)
               ~~~~~~~~^^^^^^
  File "/home/quentin/dev/QSA/pint_0.x/.venv/lib/python3.13/site-packages/mypy/types.py", line 1684, in accept
    return visitor.visit_instance(self)
           ~~~~~~~~~~~~~~~~~~~~~~^^^^^^
  File "/home/quentin/dev/QSA/pint_0.x/.venv/lib/python3.13/site-packages/mypy/type_visitor.py", line 560, in visit_instance
    return self.query_types(t.args)
           ~~~~~~~~~~~~~~~~^^^^^^^^
  File "/home/quentin/dev/QSA/pint_0.x/.venv/lib/python3.13/site-packages/mypy/type_visitor.py", line 628, in query_types
    return any(t.accept(self) for t in types)
  File "/home/quentin/dev/QSA/pint_0.x/.venv/lib/python3.13/site-packages/mypy/type_visitor.py", line 628, in <genexpr>
    return any(t.accept(self) for t in types)
               ~~~~~~~~^^^^^^
  File "/home/quentin/dev/QSA/pint_0.x/.venv/lib/python3.13/site-packages/mypy/types.py", line 1684, in accept
    return visitor.visit_instance(self)
           ~~~~~~~~~~~~~~~~~~~~~~^^^^^^
RecursionError: maximum recursion depth exceeded
/home/quentin/dev/QSA/pint_0.x/.venv/lib/python3.13/site-packages/pint/facets/numpy/quantity.py:63: note: use --pdb to drop into pdb
RecursionError: maximum recursion depth exceeded

To Reproduce

I narrowed down the issue to this single import of pint.facets.plain.quantity.PlainQuantity. Run mypy on a file with this content:

python

from pint.facets.plain.quantity import PlainQuantity

Your Environment

Issue appears since version 0.26 of pint when they introduced massive type annotations for PlainQuantity. See https://github.com/hgrecco/pint/pull/2302 and https://github.com/hgrecco/pint/pull/2303

Mypy version used: 2.3.1 and 1.9.1
Mypy command-line flags: none
Mypy configuration options from mypy.ini (and other config files): none
Python version used: 3.13.12
Operating system and version: Fedora 43 in WSL2

Source: python/mypy

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