Incompatible types in assignment for property setter

[tamuhey]

Note: if you are reporting a wrong signature of a function or a class in
the standard library, then the typeshed tracker is better suited
for this report: https://github.com/python/typeshed/issues

Please provide more information to help us understand the issue:

• Are you reporting a bug, or opening a feature request?

bug

• Please insert below the code you are checking with mypy,
  or a mock-up repro if the source is private. We would appreciate
  if you try to simplify your case to a minimal repro.

from typing import List, Iterable

class Foo:
    @property
    def x(self) -> List[int]:
        ...

    @x.setter
    def x(self, new_x: Iterable[int]):
        ...

foo = Foo()
foo.x = (1, 2, 3) # error: Incompatible types in assignment (expression has type "Tuple[int, int, int]", variable has type "List[int]")

• What is the actual behavior/output?

error: Incompatible types in assignment (expression has type "Tuple[int, int, int]", variable has type "List[int]")

• What is the behavior/output you expect?

No error because setter requires Iterable[int], not List[int]

• What are the versions of mypy and Python you are using?
  Do you see the same issue after installing mypy from Git master?

master

• What are the mypy flags you are using? (For example --strict-optional)

no flag

• If mypy crashed with a traceback, please paste
  the full traceback below.

foo.py:13: error: Incompatible types in assignment (expression has type "Tuple[int, int, int]", variable has type "List[int]")
Found 1 error in 1 file (checked 1 source file)

[bsdtux]

We are having a similar issue. We are taking a str_date and a format and trying to do a strptime
but we keep getting the error of

error: Incompatible types in assignment (expression has type "datetime", variable has type "str")

The below section of code is where we are getting the error from

date_formats = ['%Y-%m-%d %H:%M:%S.%f', '%Y-%m-%d %H:%M:%S', '%Y-%m-%d']
event_dates = {
        "date_1": event_date_1,
        "date_2": event_date_2
    }
for key, date in event_dates.items():
    for date_format in date_formats:
        try:
            date = datetime.strptime(date, date_format) # This is the offending line
            if date < datetime.strptime('1900-01-01', '%Y-%m-%d'):
                event_dates[key] = None
        except (ValueError, TypeError):
            pass

[hauntsaninja]

@bsdtux I think your issue is unrelated; pretty sure you're running into https://mypy.readthedocs.io/en/stable/common_issues.html#redefinitions-with-incompatible-types. You might be able to get around it by renaming the variable (to, eg, date_str) or using --allow-redefinition

[bsdtux]

@bsdtux I think your issue is unrelated; pretty sure you're running into https://mypy.readthedocs.io/en/stable/common_issues.html#redefinitions-with-incompatible-types. You might be able to get around it by renaming the variable (to, eg, date_str) or using --allow-redefinition

thanks @hauntsaninja it looks like what it was upset about was that we were taking the date variable in the loop and going from a string to a date object. So after taking your advice we change the date in the for loop to be date_str and the date variable holding the output of strptime was changed to new_date and now mypy is happy.

[bsdtux]

@tamuhey I wonder if yours is the same where you define the x property of having a list type but then on the setter, you are saying it takes an iterable. What happens if you set the getter for x to be type iterable as well?

[tamuhey]

What happens if you set the getter for x to be type iterable as well?

The users of Foo must rewrite their code. List is assinable to Iterable but Iterable is not assinable to List.

[hauntsaninja]

This is a duplicate of #3004 (also linking #8084 and #220)