NamedTuple.__init__(**kwargs) doesn't type check

[csingley]

• Are you reporting a bug, or opening a feature request?
  • Bug
• Please insert below the code you are checking with mypy,

from typing import NamedTuple, Optional
from collections import OrderedDict

class Datum(NamedTuple):
    id: Optional[str] = None
    value: Optional[int] = None

# This passes type checking
# datum = Datum(value=1, id="foo")

# This fails to type check
attrs = {"id": "foo", "value": 1}

# This passes type checking
# attrs = OrderedDict([("id", "bar"), ("value", 1)])

datum = Datum(**attrs)

• What is the actual behavior/output?

test.py:19: error: Argument 1 to "Datum" has incompatible type "**Dict[str, object]"; expected "Optional[str]"
test.py:19: error: Argument 1 to "Datum" has incompatible type "**Dict[str, object]"; expected "Optional[int]"

• What is the behavior/output you expect?
  • mypy should treat dict unpacking the same as keyword assignment for NamedTuple.__init__()
• What are the versions of mypy and Python you are using?
  • Python 3.7.3
  • mypy 0.701
• Do you see the same issue after installing mypy from Git master?
  • yes
• What are the mypy flags you are using? (For example --strict-optional)
  • none

I didn't see this issue reported; sorry if I overlooked. Using **OrderedDict is a workaround. as shown in the code sample above.

[antonagestam]

To clarify: this is a false positive. This is the smallest piece of code I managed to reproduce it with. Having a NamedTuple with only one field does not trigger this.

from typing import NamedTuple


class A(NamedTuple):
    a: str
    b: int


A(**{"b": 1, "a": "foo"})

Output:

test-namedtuple-fail.py:9: error: Argument 1 to "A" has incompatible type "**Dict[str, object]"; expected "str"
test-namedtuple-fail.py:9: error: Argument 1 to "A" has incompatible type "**Dict[str, object]"; expected "int"

I also see the same behavior with master (mypy-0.710+dev.b3420c8b31875fac74895d4024ad9f8f0bd2240d), and with --new-semantic-analyzer.

[ilevkivskyi]

This is not specific to named tuples, duplicate of #5382