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self-referential NamedTuple leads to spurious "incompatible types" with List[<nothing>] #3731
Description
This code typechecks cleanly:
from typing import List, NamedTuple
class Person(NamedTuple):
name: str
age: int
people: List[Person] = []
But add a self-referential attribute to the NamedTuple:
from typing import List, NamedTuple
class Person(NamedTuple):
name: str
age: int
kids: List['Person']
people: List[Person] = []
And now we get:
namedtuple.py:9: error: Incompatible types in assignment (expression has type List[<nothing>], variable has type List[Person])
If Person is an ordinary class instead of a NamedTuple, the error doesn't appear.
Activity
carljm commentedon Jul 18, 2017
For added fun, if you then do
people.append(Person(...)), you get the delightful error message:namedtuple.py:10: error: Argument 1 to "append" of "list" has incompatible type "Person"; expected "Person"ilevkivskyi commentedon Jul 18, 2017
Sorry, this is an old problem. Also there are similar things with other "synthetic types"
TypedDict,NewType, aliases etc. that don't work well in the forward-reference context. I was going to work on this, but didn't get to it yet. I will keep this open, since here you provide use-cases that are not mentioned in other issues.camio commentedon Aug 26, 2017
I ran into this issue as well, but the error message I received is slightly different.
I get this error:
ilevkivskyi commentedon Sep 29, 2017
All examples now work correctly, this is also fixed by #3952. Only an (expected) warning about not fully supported recursive type is emitted.