adding static type checking via mypy

[rasbt]

Add type hints (see PEP484) and static type checking to Travis CI using mypy.

• however, the question is whether we want to use the full type-hinting syntax (and maybe lose compatibility with older python versions) or just the type-hinting via comments. e.g.,

def hello(r: int, c=5) -> str:
   s = 'hello'  # type: str
   return '(%d + %d) times %s' % (r, c, s)

vs.

def hello(r, c=5):
   s = 'hello'  # type: str
   return '(%d + %d) times %s' % (r, c, s)

Any thoughts?

UPDATE:

As Daniel Moisset from machinalis pointed out, a Python 2.x compatible alternative to the first scenario above would be:

def hello(r, c=5):
    # type: (int, int) -> str
    """Some docstring"""
    s = 'hello'
    return '(%d + %d) times %s' % (r, c, s)

or for longer parameter lists:

def hello(r,  # type: int
          c=5):
    # type: (...) -> str
    s = 'hello'
    return '(%d + %d) times %s' % (r, c, s)

which would be the best option for now imho.

Also see his awesome blog post for more info on using mypy: http://www.machinalis.com/blog/a-day-with-mypy-part-1/