[FIXED] Why does 2d index update a list but not 1d?

Issue

I am trying to understand indexing in a list. I try:

x= [1,2,3,[4]]
x[0]=[34]
x[3][0]=95

which gives

[1, 2, 3, [95]]

but why is it not:

[34 2, 3, [95]]

? Edit: apologies my code was:

x= [1,2,3,[4]]
y=list(x)
x[0]=[34]
x[3][0]=95
print (y)

Which gives the results I stated.

Solution

In this case, I believe python list mutability doing strange things.

When you call

y = list(x)

It copies each element in the list x over to the list y.

This means it avoids mutability in the first dimension, but because the third element is copied normally under the hood, and it is a list, it remains mutable.

You can find out a bit more in the docs (https://docs.python.org/3/library/stdtypes.html#list)

Also, as others have pointed out, you are setting

x[0] = [34]

Which sets the first element of x to a list, not a number so x would actually be

[ [34], 2, 3, [95] ]

Answered By - not a tshirt