There are many different ways to split arrays, but commonly this method is used in creating training and testing sets in neural networks.
from numpy import array
a = array([[1,2,3,4,5],[6,7,8,9,10],[11,12,13,14,15],[16,17,18,19,20]])
print (a.shape)
# make 2 new arrays from array a
# array X will be everything up to and including the first x element
# array y will be everything after the first x element
X, y = a[:1,...], a[1:,...]
print (X)
print (y)
(4, 5)
[[1 2 3 4 5]]
[[ 6 7 8 9 10]
[11 12 13 14 15]
[16 17 18 19 20]]