Though it isn’t well known, there is a function designed just for this purpose, operator.methodcaller:
>>> from operator import methodcaller
>>> a = ['2011-12-22 46:31:11','2011-12-20 20:19:17', '2011-12-20 01:09:21']
>>> list(map(methodcaller("split", " "), a))
[['2011-12-22', '46:31:11'], ['2011-12-20', '20:19:17'], ['2011-12-20', '01:09:21']]
This technique is faster than equivalent approaches using lambda expressions.