Accessing key in factory of defaultdict

Question

I am trying to do something similar to this:

from   collections import defaultdict
import hashlib

def factory():
    key = \'aaa\'
    return { \'key-md5\' : ha         


        

Answer 1

__missing__ of defaultdict does not pass key to factory function.

If default_factory is not None, it is called without arguments to provide a default value for the given key, this value is inserted in the dictionary for the key, and returned.

Make your own dictionary class with custom __missing__ method.

>>> class MyDict(dict):
...     def __init__(self, factory):
...         self.factory = factory
...     def __missing__(self, key):
...         self[key] = self.factory(key)
...         return self[key]
... 
>>> d = MyDict(lambda x: -x)
>>> d[1]
-1
>>> d
{1: -1}