While loop causing problem with variables in python

Asked Mar 25 '22 at 21:19

Active Mar 25 '22 at 21:19

Viewed 31 times

I am doing 'The Longest Possible Prefix' problem on LeetCode and to solve it I have implemented the code:

strs = ["flower","flow","flight"]
s = ['']
b = []
a = 1
while s.count(s[0])==len(s) and s[0] != strs[0]:
    b = s
    s.clear()
    for i in strs:
        s.append(i[0:a])
    a+=1
print(b[0])

I have used an extra variable b to keep a previous version of the list s before I update it. The problem is that even when the while loop has broken b has again been set to the value of s giving a value that I don not want. Why is this happening and how could I fix it?

asked Mar 25 '22 at 21:19

Manav Desai

1

Your problem is with references versus values. Lists pass by reference so your `b` is effectively _the same piece of memory_ as `s` – Maximilian Burszley Mar 25 '22 at 21:23
You need `b = s.copy()` – mozway Mar 25 '22 at 21:29

While loop causing problem with variables in python

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