[FIXED] python: dynamic keys in nested dictionary

Issue

i am using the django shell to try to create such a dictionary:

{'TITLE SECTION ONE': 
  {'Category One': [element one],
  'Category Two': [element one,
                  <element two},
 'TITLE SECTION TWO': 
  {'Category One': [element one,
                   element two}

but this pieces of code: dict[section][category] = [x] change the "price element one" in "two" like the result below.

dict = dict()
for x in price.objects.all():
   if section not in dict:
       dict[section] = {
       category: [x]
   }
   else:
        dict[section][category] = [x]
        dict[section][category].append(x)




    {'TITLE SECTION ONE': 
      {'Category One': [element two],
      'Category Two': [element two,
                      element two},
     'TITLE SECTION TWO': 
      {'Category One': [element two,
                       element two}}

how can you keep all the elements?

Solution

You should only construct a new list if the category is not yet defined in the mydict[section, so:

mydict = {}
for x in price.objects.all():
    if section not in mydict:
         mydict[section] = { category: [x] }
    elif category not in mydict[section]:
         mydict[section][category] = [x]
    else:
         mydict[section][category].append(x)

another option is to work with a defaultdict:

from collections import defaultdict

mydict = defaultdict(lambda: defaultdict(list))
for x in price.objects.all():
    mydict[section][category].append(x)

mydict = {k: dict(v) for k, v in mydict.items()}

---

Note: Please do not name a variable dict, it overrides the reference to the dict builtin function [Python-doc]. Use for example mydict.

Answered By - Willem Van Onsem