Changing one dict value changes all values

dictionary, list, python

Solution

Because each key gets the same list... To make a shallow copy of the list, use the following syntax:

for k in range(10):
    a[k] = td[:]

Demo:

>>> d = {}
>>> el = [1, 2, 3]
>>> d[0] = el
>>> d[1] = el
>>> map(id, d.values())
[28358416, 28358416]

Problem

I am seeing some unusual behavior in Python dictionary: ``` import numpy as np td =[np.Inf, 2, 3] a = {} # First initialize contents of dictionary to a list of values for k in range(10): a[k] = td # now I want to access the contents to modify them based on certain criteria for k in range(10): c = a[k] c[0] = k a[k] = c ``` From this I would expect each first item of the list for each dictionary key value to be changed based on (`c[0] = k`), however, what I get at the end is that all values of the dictionary are updated to the last value of `k`, as in: ``` {0: [9, 2, 3], 1: [9, 2, 3], 2: [9, 2, 3], 3: [9, 2, 3], 4: [9, 2, 3], 5: [9, 2, 3], 6: [9, 2, 3], 7: [9, 2, 3], 8: [9, 2, 3], 9: [9, 2, 3]} ``` Am I missing something, or there is something wrong in the dictionary definition? I can work around this in a different way for my code to run, but I am interested as to why the dictionary class would behave this way.

Original source