bug: mypy error in merge() — type assignment mismatch

[FBumann]

Description

mypy reports an error on master at expressions.py:2387:

linopy/expressions.py:2387: error: Incompatible types in assignment
  (expression has type "type[QuadraticExpression] | type[LinearExpression]",
   variable has type "type[GenericExpression]")  [assignment]

The cls parameter of merge() is typed as type[GenericExpression], but when cls is None, it gets reassigned to either QuadraticExpression or LinearExpression — both concrete subclasses, which mypy considers incompatible with the declared type.

Location

linopy/expressions.py:2343-2387:

def merge(
    ...
    cls: type[GenericExpression] = None,  # type: ignore
    ...
):
    ...
    if cls is None:
        cls = QuadraticExpression if has_quad_expression else LinearExpression  # error

Environment

• linopy: master (36bc106)
• mypy: 1.20.1

[FBumann]

Fixed by #647 using cast().