script switches two items in list after for loop?

Question

I am normalizing items in lists by given numbers so eg:

l = [79, 65, 42, 63, 48, 6, 44, 31, 22, 40, 3] 
v = 79 
l = [1.0, 0.8227848101265823, 0.5316455696202531, 0.7974683544303798, 0.6075949367088608, 0.0759493670886076, 0.5569620253164557, 0.3924050632911392, 0.27848101265822783, 0.5063291139240507, 0.0379746835443038]

for that, I was using the following function:

def normalize(l, n): 
    for i in l: 
        if n == 0: 
            l[l.index(i)] = 0 
        else: l[l.index(i)] = i/n

this worked for all but one list/value combinations:

l =[48, 68, 30, 70, 83, 4, 58, 30, 27, 49, 1] 
v = 83 
l = [0.5783132530120482, 0.8192771084337349, 0.3614457831325301, 0.8433734939759037, 0.012048192771084338, 0.04819277108433735, 0.6987951807228916, 0.3614457831325301, 0.3253012048192771, 0.5903614457831325, 1]

in this last one, results for index 4 and 10 are switched, so that it presents as if 83/83= 0.012 and 1/83 = 1

now - I've already solved the problem by returning a new list instead of altering the one from the global scope, I have however not the slightest clue why this switch was happening and why it only affected this one instance. I thought it might be that the integer 30 appeared twice in the list, but after altering one appearance of it to something else not in the list already, the switch still happened.

I am still fairly new to coding and would love to know what I did wrong!

Answer 1

Looks like you just want to divide each element in the list by some variable except if that variable is zero, set the element to zero.

If that's the case then a simple list comprehension would work:

l = [79, 65, 42, 63, 48, 6, 44, 31, 22, 40, 3] 
v = 79 

def normalise(l, v):
    return [x / v for x in l] if v != 0 else [0.0] * len(l)

print(normalise(l, 0))
print(normalise(l, v))

Output:

[0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0]
[1.0, 0.8227848101265823, 0.5316455696202531, 0.7974683544303798, 0.6075949367088608, 0.0759493670886076, 0.5569620253164557, 0.3924050632911392, 0.27848101265822783, 0.5063291139240507, 0.0379746835443038]

Note:

The function will return a new list - i.e., the input list will not be modified