The name of the 2nd parameter to itertools.groupby() is documented inconsitently. Sometimes it's "key", sometimes "keyfunc". The code actually uses "key", so I adapted all occurences I found to "key".

>>> from itertools import groupby
>>> groupby.__doc__
'groupby(iterable[, keyfunc]) -> create an iterator which returns\n(key, sub-iterator) grouped by each value of key(value).\n'

>>> groupby([], keyfunc=lambda x: x)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: 'keyfunc' is an invalid keyword argument for this function

>>> groupby([], key=lambda x: x)
<itertools.groupby object at 0x7fee025d2048>