dictionary - Pythonic way to update nested dictionaries in Python -

i have data this:

featurename,machine,licensehost feature1,host1,lichost1 feature1,host2,lichost1 feature2,host1,lichost2 feature1,host1,lichost1 

and on...

i want maintain nested dictionary first level of key feature name, next machine name, license host, , value number of times combination occurs.

something like:

dictionary['feature1']['host1']['lichost1'] = 2 dictionary['feature1']['host2']['lichost1'] = 1 dictionary['feature2']['host1']['lichost2'] = 1 

the obvious way of creating/updating such dictionary (assuming reading data line line csv):

for line in file:     feature, machine, license = line.split(',')     if feature not in dictionary:         dictionary[feature] = {}     if machine not in dictionary[feature]:         dictionary[feature][machine] = {}     if license not in dictionary[feature][machine]:         dictionary[feature][machine][license] = 1     else:         dictionary[feature][machine][license] += 1 

this ensures never run key not found errors @ level.

what best way above (for number of nested levels) ?

you use defaultdict:

from collections import defaultdict import csv  def d1(): return defaultdict(int) def d2(): return defaultdict(d1) def d3(): return defaultdict(d2) dictionary = d3()  open('input.csv') input_file:     next (input_file);     line in csv.reader(input_file):         dictionary[line[0]][line[1]][line[2]] += 1  assert dictionary['feature1']['host1']['lichost1'] == 2 assert dictionary['feature1']['host2']['lichost1'] == 1 assert dictionary['feature2']['host1']['lichost2'] == 1 assert dictionary['invalidfeature']['host1']['lichost1'] == 0 

if multiple function defs bother you, can same thing more succinctly:

dictionary = defaultdict(lambda: defaultdict(lambda: defaultdict(int)))