Many levels of keys and values ​​in Python

Question

I wanted to know if the function I'm trying to implement in python is possible.

I have a global hash called Creatures. Creatures contain sub-hashes called mammals, amphibians, birds, insects.

Mammals have sub-hashes called whales, elephants. Amphibians have sub-hashes called frogs, larvae. Birds have sub-hashes called Eagles, the parrot. Insects have sub-hashes called dragonflies, mosquitoes.

Again, eagles have sub-hashes called men, women.

I count the frequencies of all these creatures from a text file. For example, if the file is in the format below:

Birds Eagle Female Mammals whales Male Birds Eagle Female I should output Creatures[Birds[Eagle[Female]]] = 2 Creatures[mammals[Whales[Male]]] = 1 

Is this possible in Python? How can I do that? I am very new to Python and please help. I am comfortable with dictionaries only up to level 1, i.e. Key-> value. But there are several keys and several values. I am not sure how to do this. I am using python 2.6. Thanks at advace!

Answer 1

If you just need to "count" things - and if the data file contains all the necessary level of "hashes" - this will do the trick:

 import collections result = collections.defaultdict(int) with open("beast","rt") as f: for line in f: hashes = line.split() key = '-'.join(hashes) result[key] += 1 print result 

Result: defaultdict(<type 'int'>, {'Mammals-whales-Male': 1, 'Birds-Eagle-Female': 2})

If you need a nested dictionary - post-processing of this result is still possible ...

Answer 2

The value assigned to a key in a dictionary can itself be another dictionary

 creatures = dict() creatures['birds'] = dict() creatures['birds']['eagle'] = dict() creatures['birds']['eagle']['female'] = 0 creatures['birds']['eagle']['female'] += 1 

However, you need to explicitly create each dictionary. Unlike Perl, Python does not automatically create a dictionary when you try to process the value of an unassigned key as such.

Unless, of course, you are using defaultdict :

 from collections import defaultdict creatures = defaultdict( lambda: defaultdict(lambda: defaultdict( int ))) creatures['birds']['eagle']['female'] += 1 

For arbitrary nesting levels, you can use this recursive definition.

 dd = defaultdict( lambda: dd ) creatures = dd creatures['birds']['eagle']['female'] = 0 

In this case, you need to explicitly initialize the integer value, since otherwise the value of creatures['birds']['eagle']['female'] will be considered another defaultdict :

 >>> creatures = dd >>> type(creatures['birds']['eagle']['female']) <class 'collections.defaultdict'> 

Answer 3

Not elegant, but working:

 result = {} for line in input_file.split("\n"): curdict = result values = line.split(" ") for item in values[:-1]: if item not in curdict: curdict[item] = {} curdict = curdict[item] last_item = values[-1] if last_item not in curdict: curdict[last_item] = 0 curdict[last_item] += 1 

This can probably be written in a cleaner way, but at least it works and allows an arbitrary level of nesting if you do not have another level of nesting for the same “entity” (for example, Birds Eagle Female and Birds Eagle do not will work )