问题
I have a variable path, which should be a tuple of strings. I want to start with it set to an empty tuple, but mypy complains.
path: Tuple[str] = ()
The error is:
Incompatible types in assignment (expression has type "Tuple[]", variable has type "Tuple[str]")
How can I assign an empty tuple to a typed variable?
Motivation
The reason I want to do this is: I want to build up the tuple dynamically, and tuples (unlike lists) can be used as dictionary keys. For example (not what I'm actually doing):
for line in fileob:
path += (line,)
some_dict[path] = some_object
This works well, except that mypy doesn't like the type declaration above. I could use a list and then convert it to a tuple, but it complicates the code.
回答1:
EDIT:
You can define a variable length, homogenous tuple like this:
Tuple[str, ...]
You can also create a "a or b" type variable with typing.Union:
from typing import Union
path: Union[Tuple[()], Tuple[str]] = ()
OLD ANSWER:
By trying to assign an empty tuple to a variable that you have typed to not allow empty tuples, you're effectivly missing the point of typing variables.
I assume that the empty tuple you are trying to assign is just a token value, and that you intend to reassign the variable later in the code (to a tuple that contains only strings.)
In that case, simply let the token value be a tuple that contains a string:
path: Tuple[str] = ('token string')
This should stop the error message.
来源：https://stackoverflow.com/questions/57566353/incompatible-types-when-assigning-an-empty-tuple-to-a-specialised-variable