How to set first N elements of array to zero?

Question

I have a long array:

x= ([2, 5, 4, 7, ...])

for which I need to set the first N elements to 0. So for N = 2, the desired output would be:

x = ([0, 0, 4, 7, ...])

Is there an easy way to do this in Python? Some numpy function?

Answer 1

Pure python:

x[:n] = [0] * n

with numpy:

y = numpy.array(x)
y[:n] = 0

also note that x[:n] = 0 does not work if x is a python list (instead of a numpy array).

It is also a bad idea to use [{some object here}] * n for anything mutable, because the list will not contain n different objects but n references to the same object:

>>> a = [[],[],[],[]]
>>> a[0:2] = [["a"]] * 2
>>> a
[['a'], ['a'], [], []]
>>> a[0].append("b")
>>> a
[['a', 'b'], ['a', 'b'], [], []]

Answer 2

Just set them explicitly:

x[0:2] = 0