setdefault

I am writing code for an application where performance is important. I am wondering why defaultdict seems to be faster then setdefault . I would like to be able to use setdefault , mostly because i do not like the print output of the nested defaultdict (see implementation below). In my code, i need to test if element_id is already a key of the dict. Here are the two functions that i am testing: def defaultdictfunc(subcases,other_ids,element_ids): dict_name= defaultdict(lambda: defaultdict(lambda: defaultdict(dict))) for subcase in subcases: for other_id in other_ids: for element_id in element

I've seen other Python programmers use defaultdict from the collections module for the following use case: from collections import defaultdict s = [('yellow', 1), ('blue', 2), ('yellow', 3), ('blue', 4), ('red', 1)] def main(): d = defaultdict(list) for k, v in s: d[k].append(v) I've typically approached this problem by using setdefault instead: def main(): d = {} for k, v in s: d.setdefault(k, []).append(v) The docs do in fact claim that using defaultdict is faster , but I've seen the opposite to be true when testing myself: $ python -mtimeit -s "from withsetdefault import main; s = [('yellow

The following two expressions seem equivalent to me. Which one is preferable? data = [('a', 1), ('b', 1), ('b', 2)] d1 = {} d2 = {} for key, val in data: # variant 1) d1[key] = d1.get(key, []) + [val] # variant 2) d2.setdefault(key, []).append(val) The results are the same but which version is better or rather more pythonic? Personally I find version 2 harder to understand, as to me setdefault is very tricky to grasp. If I understand correctly, it looks for the value of "key" in the dictionary, if not available, enters "[]" into the dict, returns a reference to either the value or "[]" and