Typeshed[1] identifies the types of all builtins for all current (2.7+) versions of python.

[1] https://github.com/python/typeshed/

0.to_string() / 5

map([1, 2, 3], lambda n: n * 2).some_field_that_doesnt_exist

A type checker would find both mistakes very easily, by only using the information from the standard library.