How do I return the positions of multiple items in a list? (Python)

Question

I am using a large data set (approx 3600 x values & 3600 y values), and am trying to return the position of certain x values corresponding to y values that have already been pulled out of the original data.

for n in new_y:
    if new_y in y:
        new_x.append(index(y))
print(new_x)

The error code I get states: :43: DeprecationWarning: elementwise comparison failed; this will raise an error in the future. if new_y in y:

Edit: I should have mentioned that when printing new_x, an empty list is returned ([])

Answer 1

You should use enumerate:

new_x = []
for i, n in enumerate(new_y):
    if n in y:
        new_x.append(i)
print(new_x)

Or, more succinctly:

new_x = [i for i, n in enumerate(new_y) if n in y]

Answer 2

Use numpy library that way you can slice the data wihtout iterating through the "dataset".