Description
Bug Report
When a generic type defined via TypeVar is used with constrained types, a base class for those types is computed and errors are reported against that base class.
To Reproduce
In this example, get() uses some internal logic to select a constructor, which is either D1 or D2, and add() constructs the specified instance, performs some work with it and returns it to the caller.
from typing import TypeVar
from random import random
class B: ...
class D1(B):
def __repr__(self)->str: return "D1 class"
class D2(B):
def __repr__(self)->str: return "D2 class"
Q = TypeVar("Q", D1, D2) # triggers error 1, 2
#Q = TypeVar("Q", bound=B) # triggers error 2
#Q = TypeVar("Q") # triggers error 2
def add(c: type[Q])->Q:
return c()
def get() -> type[D1]|type[D2]:
return D1 if random() > 0.5 else D2
# [1] error: Value of type variable "Q" of "add" cannot be "B" [type-var]
# [2] error: Incompatible types in assignment (expression has type "B", variable has type "D1 | D2")
w: D1|D2 = add(get())
print(w)Expected Behavior
No errors should be reported because all referenced types align against one another and the base class B plays no role in this code. Moreover, if B is removed as a base class of D1 and D2, the errors are still reported, but against object instead of B.
I expect TypeVar with this constraint to behave as if add() is defined as below, which reports no errors.
def add(c: type[D1]|type[D2])->D1|D2:
return c()Actual Behavior
main.py:24: error: Value of type variable "Q" of "add" cannot be "B" [type-var]
main.py:24: error: Incompatible types in assignment (expression has type "B", variable has type "D1 | D2") [assignment]
Your Environment
- Mypy version used: 1.5.1
- Mypy command-line flags: --strict --check-untyped-defs --strict-equality --warn-redundant-casts --warn-incomplete-stub --warn-unreachable --install-types --non-interactive
- Mypy configuration options from
mypy.ini(and other config files): N/A (none) - Python version used: 3.10