What's the best way to initialize a dict of dicts in Python? [duplicate]

Question

A lot of times in Perl, I'll do something like this:

$myhash{foo}{bar}{baz} = 1 

How would I translate this to Python? So far I have:

if not 'foo' in myhash:     myhash['foo'] = {} if not 'bar' in myhash['foo']:     myhash['foo']['bar'] = {} myhash['foo']['bar']['baz'] = 1 

Is there a better way?

Answer 1

If the amount of nesting you need is fixed, collections.defaultdict is wonderful.

e.g. nesting two deep:

myhash = collections.defaultdict(dict) myhash[1][2] = 3 myhash[1][3] = 13 myhash[2][4] = 9 

If you want to go another level of nesting, you'll need to do something like:

myhash = collections.defaultdict(lambda : collections.defaultdict(dict)) myhash[1][2][3] = 4 myhash[1][3][3] = 5 myhash[1][2]['test'] = 6 

edit: MizardX points out that we can get full genericity with a simple function:

import collections def makehash():     return collections.defaultdict(makehash) 

Now we can do:

myhash = makehash() myhash[1][2] = 4 myhash[1][3] = 8 myhash[2][5][8] = 17 # etc