“Protocols cannot be used with isinstance()” - why not?

Question

The new typing module contains several objects with names like \"SupportsInt\" (-Float, -Bytes, etc.). The name, and the descriptions on the documentation page for

Answer 1

As the documentation says: At runtime, isinstance(x, T) will raise TypeError. In general, isinstance() and issubclass() should not be used with types. ( https://docs.python.org/3/library/typing.html?highlight=typing#typing.TypeVar )