Datetime Issue in Windows

[ericspod]

Using datetime.datetime produces objects whose timestamp() value is not valid under Windows, at least insofar as Python calculates it. To replicate:

import datetime

dt=datetime.datetime(1970,1,2)
print(dt.timestamp())  # valid

dt=datetime.datetime(1969,1,2)
print(dt.timestamp())  # raises OSError: [Errno 22] Invalid argument

dt_delta=(dt - datetime.datetime(1970, 1, 1))
print(dt.total_seconds())  # works to produce the correct timestamp

What's going on here is the default datetime object doesn't handle timestamps correctly for dates before Jan 2 1970 and after Jan 19 3001. By subtracting the epoch (Jan 1 1970) from a datetime this produces a timedelta object whose total_seconds method returns the timestamp that is expected. A routine is required to get the correct timestamp that will be portable across platforms:

def timestamp(dt):
    return (dt - datetime.datetime(1970, 1, 1)).total_seconds()

This should be used in place of calling the datetime.datetime.timestamp method. However, datetime.datetime.fromtimestamp will not work with these values, a function to do this needed as well:

def fromtimestamp(ts):
    return datetime.datetime(1970, 1, 1) + datetime.timedelta(seconds=ts)

[ericspod]

We do need to change our tests to cover the three platforms.