Python Append items to dictionary in a loop

I am trying to append values to a dictionary inside a loop, but somehow it’s only appending one of the values. I recreated the setup using the same numbers I am dynamically getting.

The output from "print(vertex_id_from_shell)" is "{0: [4], 1: [12], 2: [20]}". I need to keep the keys, but add the remaining numbers to the values.

Thanks.

shells = {0: [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13], 1: [14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27], 2: [28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41]}
uvsID = [0, 1, 3, 2, 2, 3, 5, 4, 4, 5, 7, 6, 6, 7, 9, 8, 1, 10, 11, 3, 12, 0, 2, 13, 14, 15, 16, 17, 17, 16, 18, 19, 19, 18, 20, 21, 21, 20, 22, 23, 15, 24, 25, 16, 26, 14, 17, 27, 28, 29, 30, 31, 31, 30, 32, 33, 33, 32, 34, 35, 35, 34, 36, 37, 29, 38, 39, 30, 40, 28, 31, 41]
vertsID = [0, 1, 3, 2, 2, 3, 5, 4, 4, 5, 7, 6, 6, 7, 1, 0, 1, 7, 5, 3, 6, 0, 2, 4, 8, 9, 11, 10, 10, 11, 13, 12, 12, 13, 15, 14, 14, 15, 9, 8, 9, 15, 13, 11, 14, 8, 10, 12, 16, 17, 19, 18, 18, 19, 21, 20, 20, 21, 23, 22, 22, 23, 17, 16, 17, 23, 21, 19, 22, 16, 18, 20]


vertex_id_from_shell = {}

for shell in shells:
    selection_shell = shells.get(shell)
    
    #print(selection_shell)
    
    for idx, item in enumerate(selection_shell):
        if item in uvsID:
            uv_index =  uvsID.index(item)
            vertex_ids = vertsID[uv_index]
            vertex_id_from_shell[shell] =  [  ( vertex_ids ) ]
    
print(vertex_id_from_shell)
#{0: [4], 1: [12], 2: [20]} 

#desired result
{0: [0, 1, 2, 3, 4, 5, 6, 7, 0, 1, 7, 0, 1, 7, 5, 6, 4], 1: [8, 9, 11, 10, 13, 12, 15, 14, 9, 8, 15, 13, 14, 12], 2: [16, 17, 19, 18, 21, 20, 23, 22, 17, 16, 23, 21, 22, 20]}

>Solution :

You are setting vertex_id_from_shell[shell] to a new list, containing only one item every time. Instead, you should append to it.
But first, of course that list needs to exist, so you should check and create it if it doesn’t already exist.

shells = {0: [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13], 1: [14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27], 2: [28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41]}
uvsID = [0, 1, 3, 2, 2, 3, 5, 4, 4, 5, 7, 6, 6, 7, 9, 8, 1, 10, 11, 3, 12, 0, 2, 13, 14, 15, 16, 17, 17, 16, 18, 19, 19, 18, 20, 21, 21, 20, 22, 23, 15, 24, 25, 16, 26, 14, 17, 27, 28, 29, 30, 31, 31, 30, 32, 33, 33, 32, 34, 35, 35, 34, 36, 37, 29, 38, 39, 30, 40, 28, 31, 41]
vertsID = [0, 1, 3, 2, 2, 3, 5, 4, 4, 5, 7, 6, 6, 7, 1, 0, 1, 7, 5, 3, 6, 0, 2, 4, 8, 9, 11, 10, 10, 11, 13, 12, 12, 13, 15, 14, 14, 15, 9, 8, 9, 15, 13, 11, 14, 8, 10, 12, 16, 17, 19, 18, 18, 19, 21, 20, 20, 21, 23, 22, 22, 23, 17, 16, 17, 23, 21, 19, 22, 16, 18, 20]


vertex_id_from_shell = {}

for shell in shells:
    selection_shell = shells.get(shell)
    
    #print(selection_shell)
    
    for idx, item in enumerate(selection_shell):
        if item in uvsID:
            uv_index =  uvsID.index(item)
            vertex_ids = vertsID[uv_index]

            # if the list does not exist, create it
            if shell not in vertex_id_from_shell:
                vertex_id_from_shell[shell] = []

            # append to list
            vertex_id_from_shell[shell].append(vertex_ids)
    
print(vertex_id_from_shell)
# {0: [0, 1, 2, 3, 4, 5, 6, 7, 0, 1, 7, 5, 6, 4],
#  1: [8, 9, 11, 10, 13, 12, 15, 14, 9, 8, 15, 13, 14, 12],
#  2: [16, 17, 19, 18, 21, 20, 23, 22, 17, 16, 23, 21, 22, 20]}