Redefinition using the same type should not be an error

Possibly related to #10563.

Bug Report

Consider the following:

# a.py

x: int = 5

# b.py

from a import *

x: int = 7 # error: Name "x" already defined (possibly by an import)  [no-redef]

I would not call it an error. Sure, it's already defined, but it was an int originally.

If you do this:

# c.py

from a import *

x: float = 7.5 # error: Name "x" already defined (possibly by an import)  [no-redef]

You get the same error, but in this case, I'd say that's correct, because maybe I didn't realize it was an int.

And this:

# d.py

from a import *

x = 'boo' # error: Incompatible types in assignment (expression has type "str", variable has type "int")  [assignment]

This I also agree with.

Expected Behavior
I would argue that I should not get an error in b.py, whereas the errors in c.py and d.py are correct.

Typehints to me are as much a documentation tool as they are indispensable to finding bugs. Not being able to reiterate that something is an int means that I cannot document it in the code. I believe this is particularly important with star-imports because by just reading the current file, you have no idea what's being imported.

Here's something else to consider:

# a.py

x: float = 3.14

# b.py

from a import *

x = 5 # no error, because 5 is a float.

Do we know that the author new that x is a float and thus 5 is OK, or did they really mean to write x: int = 5? If I were allowed to write x: float = 5, we would have a definitive answer.

• Mypy version used: 1.3.0
• Mypy configuration options from mypy.ini (and other config files): ignore_missing_imports = True
• Python version used: 3.8.10

まず、報告された mypy の設定と Python のバージョンで、a.py、b.py、c.py、d.py の例を再現します。同じ型の再定義、異なるアノテーション、互換性のない代入について診断結果を比較します。期待されるケースが一貫して区別され、報告された動作に対するリグレッションカバレッジがあれば完了です。