mypy now reports type errors after upgrading from sympy 1.9 to 1.10.1

[Arthur Ryman]

I used type hints in my sympy 1.9 application and found no type error when running mypy 0.950.

I upgraded to sympy 1.10.1 and now mypy reports lots of errors.

For example:

error: Variable "sympy.matrices.Matrix" is not valid as a type

Does anyone know what changed in 1.10.1?

Are there examples of the correct way to use type hints with sympy 1.10.1?

Thanks.

-- Arthur Ryman

[Qijia Liu]

SymPy becomes PEP 561 compatible since 1.10

See https://github.com/sympy/sympy/pull/22337

As a side effect, since SymPy is not well typed in many places, it causes false positives at downstream.

[Arthur Ryman]

Thanks. That explains the change in behavior. I looked at the PR and it appears to simply add an empty py.types file. Are there any type information stubs (.pyi files)?

Do you know of any examples of how to use type hints to indicate, e.g., Matrix args or results?

-- Arthur

[Qijia Liu]

No, currently there are no .pyi files in SymPy.

Could you please submit issues with code snippets that mypy reports error?

One workaround is to let mypy skip SymPy, just like pre-1.9 behavior. Reference: https://github.com/python/mypy/issues/7769

Here is an example that contains both error-typed numpy and sympy code:

import numpy

import sympy

nv: int = numpy.__version__

x: int = sympy.Symbol('x')

If you run mypy with it, you will get 2 errors.

Then if you create a mypy.ini as below and run mypy again, you will only get the numpy error

[mypy-sympy.*]

follow_imports = skip

follow_imports_for_stubs = True