I have a list of words and I would like to store them in a nested dictionary.
Here is the sample list:-
words = ['Apple','Ape','Bark','Barn']
The dictionary that I want to create is as follows:-
{'A':{'P':{'E':{},
'P':{'L':{'E':{}}}}},
'B':{'A':{'R':{'K':{},'N':{}}}}}
The words are case insensitive.
Use a collections.defaultdict() object instead:
from collections import defaultdict
def tree():
return defaultdict(tree)
nested = defaultdict(tree)
for word in words:
node = nested
for char in word:
node = node[char.upper()]
Whenever you try to access a key in a defaultdict that does not yet exist, the default factory is called to produce a value for that key, transparently. In the above code the default factory is tree(), which produces another defaultdict() with the same factory, letting you build up a nested set of dictionaries merely by accessing the keys.
Demo:
>>> from collections import defaultdict
>>> def tree():
... return defaultdict(tree)
...
>>> nested = defaultdict(tree)
>>> words = ['Apple','Ape','Bark','Barn']
>>> for word in words:
... node = nested
... for char in word:
... node = node[char.upper()]
...
>>> nested
defaultdict(<function tree at 0x114e62320>, {'A': defaultdict(<function tree at 0x114e62320>, {'P': defaultdict(<function tree at 0x114e62320>, {'P': defaultdict(<function tree at 0x114e62320>, {'L': defaultdict(<function tree at 0x114e62320>, {'E': defaultdict(<function tree at 0x114e62320>, {})})}), 'E': defaultdict(<function tree at 0x114e62320>, {})})}), 'B': defaultdict(<function tree at 0x114e62320>, {'A': defaultdict(<function tree at 0x114e62320>, {'R': defaultdict(<function tree at 0x114e62320>, {'K': defaultdict(<function tree at 0x114e62320>, {}), 'N': defaultdict(<function tree at 0x114e62320>, {})})})})})
>>> def print_nested(d, indent=0):
... for k, v in d.iteritems():
... print '{}{!r}:'.format(indent * ' ', k)
... print_nested(v, indent + 1)
...
>>> print_nested(nested)
'A':
'P':
'P':
'L':
'E':
'E':
'B':
'A':
'R':
'K':
'N':
A defaultdict is a subclass of the standard Python dictionary and apart from materializing values for keys automatically, behaves exactly like a regular dictionary.