python key in dict.keys() performance for large dictionaries

Question

I was wondering if you guys might be able to give me some advice in regards to making the performance of my code much better.

I have a set of for loops which look to

Answer 1

Using collections.defaultdict, this can be simplified to

d = collections.defaultdict(list)
for value in value_list:
    d[value.key].append(value.val)