There's a facility for this task called groupby
. But it uses iterators and depends on the fact that items to be grouped together are already in order, so you might need to sort the input before applying it, depending on is "sortedness" of course.
from itertools import groupby
v = [ (datetime.date(2014, 4, 15), {'first_name': 'Mike', 'last_name': 'Jackson'}),
(datetime.date(2014, 4, 15), {'first_name': 'Hannah', 'last_name': 'Jackson'}),
(datetime.date(2014, 4, 16), {'first_name': 'Tom', 'last_name': 'Jackson'}),
(datetime.date(2014, 4, 16), {'first_name': 'Macy', 'last_name': 'Jackson'}) ]
v.sort() # to ensure that all equal datetimes are together in the list
result = [ list(i) for x, i in itertools.groupby(v, lambda a: a[0]) ]
result
will then be this:
[ [ (datetime.date(2014, 4, 15), {'first_name': 'Mike', 'last_name': 'Jackson'}),
(datetime.date(2014, 4, 15), {'first_name': 'Hannah', 'last_name': 'Jackson'}) ],
[ (datetime.date(2014, 4, 16), {'first_name': 'Tom', 'last_name': 'Jackson'}),
(datetime.date(2014, 4, 16), {'first_name': 'Macy', 'last_name': 'Jackson'}) ] ]
Which is what you wanted.