how can I add an element to a nested dictionary

Question

here's my code:

import copy
    
teamdict = {1:{},2:{},3:{},4:{},5:{}}
teamlst = []
matchlst = [1,2,3,4,5]
lst = [[1,5,0],[1,0,3],[2,3,0],[2,0,1],[3,0,6],[3,0,1],[4,0,1],[4,0,5],[5,0,8]]
for i in matchlst:
    for j in lst:
        if i == j[0]:
            teamlst.append(j[2])
        elif len(teamlst)>0 and i != j:
            continue
        else:
            pass
    teamlst = set(teamlst)
    teamlst = list(teamlst)
    teamlst.sort()
    team_dictionary = dict.fromkeys(teamlst, [])
    teamdict[i] = team_dictionary
    teamlst.clear()
print(teamdict)
dic = copy.deepcopy(teamdict)

for i in lst:
    dic[i[0]][i[2]].append(i[1])
print(dic)

this is what i got:

{1: {0: [5, 0], 3: [5, 0]}, 2: {0: [3, 0], 1: [3, 0]}, 3: {1: [0, 0], 6: [0, 0]}, 4: {1: [0, 0], 5: [0, 0]}, 5: {8: [0]}}

but what i expect is:

{1: {0: [5], 3: [0]}, 2: {0: [3], 1: [0]}, 3: {1: [0], 6: [0]}, 4: {1: [0], 5: [0]}, 5: {8: [0]}}

what goes wrong? seems like this append method add the element to all the keys in the nested dictionary

It is hard to guess what your code should do. Could you add an explanation of what you are trying to do here? — Lexpj, Jan 21 '23 at 10:40
so basically I want to add a value from the list, which is i[1] to a corresponding nested dictionary based on the i[0] and i[2] — user21054862, Jan 21 '23 at 10:43
Welcome to Stack Overflow. `dict.fromkeys(teamlst, [])` makes each value in the dict be **the same** empty list; so adding to it means the change is reflected in each value. Please see the linked duplicates for details. — Karl Knechtel, Jan 21 '23 at 11:50
(For future questions, please read https://ericlippert.com/2014/03/05/how-to-debug-small-programs/ and [mre] and try to figure out exactly what part of the code is *actually causing a problem*. — Karl Knechtel, Jan 21 '23 at 12:08

score 0 · Answer 1 · answered Jan 21 '23 at 10:47

0

I assume you have created your dictionary with multiple references to the same list.

If I execute your code I get what you want.

>>> lst = [[1,5,0],[1,0,3],[2,3,0],[2,0,1],[3,0,6],[3,0,1],[4,0,1],[4,0,5],[5,0,8]]
>>> dic = {1: {0: [], 3: []}, 2: {0: [], 1: []}, 3: {1: [], 6: []}, 4: {1: [], 5: []}, 5: {8: []}}
>>> for i in lst:
...     dic[i[0]][i[2]].append(i[1])
...
>>> print(dic)
{1: {0: [5], 3: [0]}, 2: {0: [3], 1: [0]}, 3: {1: [0], 6: [0]}, 4: {1: [0], 5: [0]}, 5: {8: [0]}}

answered Jan 21 '23 at 10:47

Ruben

38
1
6

yes you are right. what should i do if I created such a dictionary with multiple references? – user21054862 Jan 21 '23 at 11:11
i tried to use deepcopy but it doesn't work – user21054862 Jan 21 '23 at 11:32
1

" what should i do if I created such a dictionary with multiple references?" If they need to be separate, then **don't** create that; make the dictionary start off with separate empty lists instead. Copying, even deep copy, cannot help here, because the copy will have the *same aliasing structure* with its own distinct group of objects. – Karl Knechtel Jan 21 '23 at 12:09

how can I add an element to a nested dictionary

1 Answers1