how to convert FunctionName(t1: datetime, t2: datetime): to Python 2

Question

There is an example located at How do I find the time difference between two datetime objects in python?

It uses

def check_time_difference(t1: datetime, t2: datetime):

as in

def check_time_difference(t1: datetime, t2: datetime):
    t1_date = datetime(
        t1.year,
        t1.month,
        t1.day,
        t1.hour,
        t1.minute,
        t1.second)

    t2_date = datetime(
        t2.year,
        t2.month,
        t2.day,
        t2.hour,
        t2.minute,
        t2.second)

    t_elapsed = t1_date - t2_date

    return t_elapsed

I'm wondering, is there a way to convert that first line so that it works with Python 2? In Python 2, I get an error that says

def check_time_difference(t1: datetime, t2: datetime):
SyntaxError: invalid syntax

It works fine in Python 3.

Answer 1

Type hints, PEP 484, are new in Python 3.5.

The code you use will work under Python 2 if you just remove them:

def check_time_difference(t1, t2):

To make it truly compatible (as in: mypy will still be able to typecheck it), add a type hint comment:

def check_time_difference(t1, t2):
    # type: (datetime, datetime) -> timedelta

As far as I can see form the mypy docs this syntax requires the return type (in this case: timedelta) to be annotated, too. In your Python 3 syntax example, it is ommitted, but it would look like:

def check_time_difference(t1: datetime, t2: datetime) -> timedelta: