python datetime.strptime: ignore fraction of a second

I'm working on converting a human readable time to a datetime object . In order to do this, I'm using datetime.datetime.strptime.

Simple enough, however, the human readable time that I have contains fractions of a second, which I'm not able to parse. If this was a constant, I could incorporate it as part of the format. However, since it is not a constant, I am unable to do so.

This is what I'm doing right now:

>>> humanTime = '2012/06/10T16:36:20.509Z'
>>> datetime.datetime.strptime(humanTime, "%Y/%m/%dT%H:%M:%SZ")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "lib/python2.7/_strptime.py", line 325, in _strptime
    (data_string, format))
ValueError: time data '2012-06-10T16:36:20.507Z' does not match format '%Y-%m-%dT%H:%M:%SZ'

So I figure that the issue here is that the fraction of a second is not parseable. I don't really care about that fraction of a second. Short of slicing the string, is there a way by which I can ask datetime to ignore the fraction of a second (preferably with the format)?

I have a feeling that I might be missing something very basic. I'd appreciate any help.