With the following example I get an error.

from mypy_extensions import TypedDict

class Test(TypedDict):
    a: str
    b: str

def read(test: Test) -> str:
    key = 'a'
    return test[key]

error: TypedDict key must be a string literal; expected one of ('a', 'b')

Can mypy not figure out that key is set to a literal?

In my own code im building up key dynamically to get a key from a TypedDict.

mypy version: 0.711