Inconsistent swapping in python

Question

I can't understand why python swapping is working differently in the following example. Could someone please explain? I'm using python 3.6.9.

i = 0
perm = [2, 0, 1, 3]
perm[i], perm[perm[i]] = perm[perm[i]], perm[i]
print(perm)
[1, 2, 1, 3]

perm = [2, 0, 1, 3]
perm[perm[i]], perm[i] = perm[i], perm[perm[i]]
print(perm)
[1, 0, 2, 3]

Does this answer your question? Understand Python swapping: why is a, b = b, a not always equivalent to b, a = a, b? — Czaporka
– Czaporka, Commented Jul 8, 2021 at 9:44

Jiaju Huang · Accepted Answer · 2020-02-22 06:38:31Z

1

In python, a,b = b,a means t = a; a = b; b = t; sequentially. In the second case, it exchange the values at index 0 and index 2.
In the first case, after assigning the value to perm[i], perm[i] became 1, so the next step become to assign value at index 0 to index 1.

answered Feb 22, 2020 at 6:38

Jiaju Huang

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