Generate a NumPy array with powers of 2

Question

Usually when creating certain sequences of numbers, python and numpy offer some syntactic sugar to do so in a simple way, without generating them yourself with for-loops, e.g. range(start, stop, step).

I'm having a rather simple problem that I'm struggling to solve in an elegant way: Generate a list of the powers of two. E.g. list = [1, 2, 4, 8, ...].

I came up with

n_powers = 4
list = np.zeros(n_powers)
for i in range(0, n_powers): 
    list[i] = 2 ** i

Is there a better way to do this?

Answer 1

You seem to be using NumPy, so why not just do this -

>>> 2 ** np.arange(4)
array([1, 2, 4, 8])

This is broadcasted exponentiation.

Answer 2

Maybe just:

l = [2**i for i in range(n)]