In python how can I set multiple values of a list to zero simultaneously?

Question

Conceptually, I want to do:

arr[20:] = 0

where arr is a list. How can I do this?

Answer 1

Here are a couple of options:

List comprehension

>>> a = [1]*50
>>> a = [aa if i < 20 else 0 for i,aa in enumerate(a)]
>>> a
[1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]

List slice assignment:

>>> a = [1]*50
>>> a[20:] = [0 for aa in a[20:]]
>>> a
[1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]

Zip(*zip):

>>> a = [1]*50
>>> a[20:] = zip(*zip(a[20:],itertools.repeat(0)))[1]