mweeks@air:Desktop$ cat short_circuit.py 
# Writen by Michael Weeks to illustrate short-cirucit evaluation.
#

# Begin lines from
# https://jakevdp.github.io/PythonDataScienceHandbook/02.02-
#   the-basics-of-numpy-arrays.html
import numpy as np

np.random.seed(0)  # seed for reproducibility
x1 = np.random.randint(10, size=6)  # One-dimensional array
# End lines from
# https://jakevdp.github.io/PythonDataScienceHandbook/02.02-
#   the-basics-of-numpy-arrays.html

xlen = x1.size;
print("xlen is ", xlen)

xindex = 5;
if (x1[xindex] == 4): 
    print("x1[", xindex, "] is four")
else:
    print("x1[", xindex, "] is not four")

xindex = xindex + 1;

# Note: xindex is now out-of-bounds
# The next if block works
if ((xindex < xlen) and (x1[xindex] == 4)): 
    print("x1[", xindex, "] is four")
else:
    print("x1[", xindex, "] is not four")

print("About to cause an error")
if ((x1[xindex] == 4) and (xindex < xlen)): 
    print("x1[", xindex, "] is four")
else:
    print("x1[", xindex, "] is not four")



mweeks@air:Desktop$ 
mweeks@air:Desktop$ python short_circuit.py 
xlen is  6
x1[ 5 ] is not four
x1[ 6 ] is not four
About to cause an error
Traceback (most recent call last):
  File "/Users/mweeks/Desktop/short_circuit.py", line 34, in <module>
    if ((x1[xindex] == 4) and (xindex < xlen)): 
         ~~^^^^^^^^
IndexError: index 6 is out of bounds for axis 0 with size 6
mweeks@air:Desktop$