Mypy complains about issues after cache is filled #11046

Bug Report

I have a simpel dot dict implementation. But if I change something in my code somewhere else, mypy complains with weird errors. My current workaround is, to delete the mypy cache before each run

To Reproduce

(Write your steps here:)

1. Clean the mypy cache
2. Create x.py

class DotDict(dict):
    __setattr__ = dict.__setitem__
    __delattr__ = dict.__delitem__
    __getattr__ = dict.get

3. mypy x.py --> works fine
4. Add a=2 to the end of x.py
5. mypy x.py --> error

x.py:2: error: Incompatible types in assignment (expression has type "Callable[[Dict[_KT, _VT], _KT, _VT], None]", base class "object" defined the type as "Callable[[object, str, Any], None]")
x.py:3: error: Incompatible types in assignment (expression has type "Callable[[Dict[_KT, _VT], _KT], None]", base class "object" defined the type as "Callable[[object, str], None]")

Expected Behavior

No error

Actual Behavior

Error; seems like a caching issue

Your Environment

• Mypy version used: 0.910
• Mypy command-line flags: nothing
• Mypy configuration options from mypy.ini (and other config files): nothing
• Python version used: 3.7.1
• Operating system and version: Linux