I don't need laziness itertools.groupby. I just want to group my list into a list of lists as such:
dict([(a, list(b)) for a,b in itertools.groupby(mylist, mykeyfunc)])
Is there a standard feature that already does this?
No, there is no function in this standard library.
It looks like you already have a one-line function that does what you want. Use it.