Python [:-1] vs remove

Question

While writing a recursive function in python, I noticed an interesting phenomenon. .append will change an input variable, but = creates a private instance variable in the function. For example, using equals does not affect a,

>>> def f(x):
        x=x[:-1]
>>> a=[1, 2, 3]
>>> f(a)
>>> a
[1, 2, 3]

while using append changes a.

>>> def g(x):
        x.remove(3)

>>> g(a)
>>> a
[1, 2]
>>> 

I assume this is because .remove edits the reference, while [:-1] creates a new list, but is there a reason why this occurs?

Answer 1

From Ned Batchelder - Facts and Myths about Python names and values - PyCon 2015:

Functions like x.append("something") and x.remove("something") mutate a value, and change their values. However, using x=x+["something"] or x=x[:-1] rebind a reference, and create a new value which the variable now points to.

Thanks to @timgeb for commenting the video!