Prevent Python from treating _Callable an iterable

[uwinx]

Problem

Due to lack of __iter__ implementation, Python is attempting to iterate over _Callable when possible. It's generally an undesired behavior, given the purposes of the _Callable class.

You can easily reproduce the issue:

[*__import__("lambdas")._]

Implementation

That should be a no-brainer to fix and write tests for.

class _Callable:
    __iter__ = None