Pretty frequently I have errors where I forget to call a method and accidentally pass a method object to % or str.format. Mypy doesn't complain since it's possible to convert a callable object to a string, though usually that's not what I want.

Example:

class Item:
    def name(self) -> str: ...

def f(x: Item) -> None:
    print('name: {}'.format(x.name))  # No error, though should be x.name() 
    print('name: %s' % x.name)  # Similar to above
    foo(str(x.name))  # Ditto

This occasionally happens during refactoring as well, when I replace an instance variable with a method.

Here are a few things we could do about this:

1. Special case these errors and generate a warning even though the code is not necessarily wrong. Maybe require an explicit repr(x.some_method) to silence the error (# type: ignore or a cast to object would also work).
2. Introduce a new strictness flag that causes these to be flagged. Not sure if this should be enabled by default.
3. Introduce a new strictness flag that catches these and other cases where there is no runtime type error, but that we suspect might be errors. Passing a string argument when an iterable object is expected comes to mind as a kind of similar issue, and there are probably others.
4. Do nothing, since there is no runtime type error and the code could well be valid.

Option 2 seems too specialized -- this doesn't seem important enough to add a strictness flag. Personally I prefer the more opinionated option 1. We could add a hint about how to silence the error in case the code happens to be correct.