Static type-checking errors caused by numbers.Real annotations

[brunopasseti]

Describe the bug

Since commit f65eb951, Python-MIP annotations uses numbers.Real for type annotations.

However, it causes false-positive in static type checkers such as mypy and Pylance.
Type checkers do not treat the numbers ABC hierarchy and virtual subclass registration as a usable static numeric type hierarchy.

To Reproduce

import mip


def main() -> None:
    model = mip.Model()
    y = model.add_var(name="y", lb=0.0, ub=1.0)
    xf_sum: mip.Var | mip.LinExpr = y
    big_m: float = 2.0

    model.add_constr(big_m * y >= xf_sum)
    model.optimize()

With Pylance type checking set to standard, this reports:

Operator "*" not supported for types "float" and "Var | LinExpr"
  Operator "*" not supported for types "float" and "Var"
  Operator "*" not supported for types "float" and "LinExpr"

Mypy shows the same limitation for numbers types:

__init__.py:6: error: Argument "lb" to "add_var" of "Model" has incompatible type "float"; expected "Real"  [arg-type]
__init__.py:6: note: Types from "numbers" are not supported for static type checking
__init__.py:6: note: See https://peps.python.org/pep-0484/#the-numeric-tower
__init__.py:6: note: Consider using a protocol instead, such as typing.SupportsFloat
__init__.py:6: error: Argument "ub" to "add_var" of "Model" has incompatible type "float"; expected "Real"  [arg-type]
__init__.py:10: error: Unsupported operand types for * ("float" and "Var")  [operator]

Expected behavior

Idk if this should be labelled as a bug or enhancement. If is a bug: float * mip.Var and float * mip.LinExpr, and everything else using numbers package should staticaly type-check without errors.

Desktop

• Operating System: Windows and Linux
• Python: 3.11.12 and 3.13.14
• Python-MIP: 1.17.4
• mypy: 2.3.1
• Pylance: 2026.3.104
• VS Code: 1.138.0
• Type-checking mode: pylance in standard

Additional context

More information can be found in the Python and the Mypy issue linked above:

• Decide what to do with numbers.Integral etc. python/typing#272
• What to do about types from the numbers module? python/mypy#2636

Fix?

Use type unions int | float, or the protocol typing.SupportsFloat, while retaining numbers.Real for runtime isinstance checks if needed.

If this behaviour isn't expected I can fork it/open a PR to fix it

[h-g-s]

Hi @brunopasseti, thanks for the detailed report!

You were right, using int | float instead of numbers.Real in the type hints was the correct fix. We just merged this change directly into master:

• Commit: 766ed33
• We added a new type alias mip.Numeric = int | float and replaced numbers.Real with it everywhere in the function/method signatures (type hints only). Actual runtime isinstance() checks still use numbers.Real, so behavior is unchanged, only the static typing got better.

This should fix the mypy/Pylance false positives from your example. It will be included in the next release. Closing this issue now, feel free to reopen if you still see problems after upgrading.

Thanks again for pointing this out!