Trying to add lists of lists to an empty dictionary in a for loop, but the entries are being completely overwritten in every iteration

Question

Novice with programming in general here. I have an empty dictionary with no number of keys, (where no in this case = 3). I'm trying to generate a list of lists that will be added to the dictionary within a loop, but over each loop the other keys are being overwritten. See my attempt below:

#generating dictionary for all fibres with number n 
fibre = {i : {}for i in range(no)}
#generating empty fibre of size n_f
fibre_e = [[[] for i in range(n_f)] for j in range(n_f)]
rand_r = [[] for a in range(no)]
rand_c = [[] for a in range(no)]

#generating fibre element from random corner elements
for a in range(no):
    # choosing a random corner element
    fibre[a] = fibre_e
    rand_r[a] = randrange(len(all_e))
    rand_c[a] = randrange(len(all_e))

    for i in range(n_f):
        e1_fibre=all_e[rand_r[a]][rand_c[a]]
        #move to upper row
        rand_r[a] += 1
        for j in range(n_f):
            fibre_e[i][j] = e1_fibre
            e1_fibre += 1

    print(fibre)

This is the output when I checked the progression:

{0: [[57, 58], [66, 67]], 1: {}, 2: {}}
{0: [[33, 34], [42, 43]], 1: [[33, 34], [42, 43]], 2: {}}
{0: [[29, 30], [38, 39]], 1: [[29, 30], [38, 39]], 2: [[29, 30], [38, 39]]}

For context, this is to generate an abaqus mesh file with a random distribution of identical fibre elements within a matrix.

edit:context

Using copy.deepcopy worked

for a in range(no):
    # choosing a random corner element

    rand_r[a] = randrange(len(all_e))
    rand_c[a] = randrange(len(all_e))

    for i in range(n_f):
        e1_fibre=all_e[rand_r[a]][rand_c[a]]
        #move to upper row
        rand_r[a] += 1
        for j in range(n_f):
            fibre_e[i][j] = e1_fibre
            e1_fibre += 1
            fibre[a] = copy.deepcopy(fibre_e)

    print(fibre)

Output:

{0: [[68, 69], [77, 78]], 1: {}, 2: {}}
{0: [[68, 69], [77, 78]], 1: [[6, 7], [15, 16]], 2: {}}
{0: [[68, 69], [77, 78]], 1: [[6, 7], [15, 16]], 2: [[28, 29], [37, 38]]}

See https://stackoverflow.com/q/2612802/8586227 – Davis Herring Oct 07 '17 at 03:04 — Davis Herring, Oct 07 '17 at 03:04
thank you. copy.deepcopy worked for me – Aedan Oct 07 '17 at 03:15 — Aedan, Oct 07 '17 at 03:15

score 1 · Answer 1 · answered Oct 07 '17 at 03:30

1

Specifically in your case, just assign the expression you're assigning to fibre_e to fibre[a] instead. Then new lists get created for each iteration. (You don't need the variable fibre_e then at all.)

answered Oct 07 '17 at 03:30

Davis Herring

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Trying to add lists of lists to an empty dictionary in a for loop, but the entries are being completely overwritten in every iteration

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