Question

In my code:

line_x = 10
c = 'A'
d = 'B'
a = {}
a['one']='|   |   |   |   |   |'
a['two']='|   |   |   |   |   |'
#untill thirteen

vak = a.keys()
b = a #copy the dictionary
spot = a[vak[0]]
spot2 = b[vak[0]]
a[vak[0]] = spot[:(line_x)]+ d+ spot[(line_x+1):]
b[vak[0]] = spot2[:(line_x)]+ c+ spot2[(line_x+1):]

print a[vak[0]] #output_a = |   |   | A |   |   |
print b[vak[0]] #output_b = |   |   | A |   |   | <- which should be a 'B' in the middle

I’m having some trouble with making a copy of a dictionary and changing a value.

When I want to change a value in one of the dictionaries, the value of both the original and the copy change. But I only want the original to change and have the copy to change to something else. I can’t seem to find the problem although it is in such a small and relatively easy code.

Answer 1

b = a doesn’t copy the dictionary, it rebinds b to point at the same object as a (so when you change a, you can observe the effect on b as well). Use b = copy.copy(a) (copy module) instead.