Simple example of some array manipulations

ian_examply.py

# from <module> import * is strongly discouraged
import numpy as np

# One way to make your array that shows off a few features
# Specifying it like you did is fine, but why bother?
a = np.arange(1, 7)
a[1::2] *= -1

# Again, just demonstrating some features
choice = np.array([np.ones(6),
                   range(1, 7)])
choice[0, -3:] = -1

# Show the arrays we ended upwith
print "a: \n", a
print "choice: \n", choice

# We want to count how many elements of `a` are > 0
# when the first row of `choice` is 1

# In one line
print "One-liner: ", (a[choice[0] == 1] > 0).sum()

# A bit more didactically
mask = choice[0] == 1
a_vals = a[mask]
a_pos = a_vals > 0
a_sum = a_pos.sum()

print "Didactic: ", a_sum