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

Unfortunately not directly, as defaultdict specifies that default_factory must be called with no arguments:

http://docs.python.org/2/library/collections.html#collections.defaultdict

But it is possible to use defaultdict as a base class that has the behavior you want:

class CustomDefaultdict(defaultdict):
    def __missing__(self, key):
        if self.default_factory:
            dict.__setitem__(self, key, self.default_factory(key))
            return self[key]
        else:
            defaultdict.__missing__(self, key)

This works for me:

>>> a = CustomDefaultdict(factory)
>>> a
defaultdict(, {})
>>> print a['aaa']
{'key-md5': '47bce5c74f589f4867dbd57e9ca9f808'}
>>> print a['bbb']
{'key-md5': '08f8e0260c64418510cefb2b06eee5cd'}