# Define a procedure, greatest,
# that takes as input a list
# of positive numbers, and
# returns the greatest number
# in that list. If the input
# list is empty, the output
# should be 0.

def greatest(xs):
    greatest = 0
    for x in xs:
        if x > greatest:
            greatest = x
    return greatest

#print greatest([4,23,1])
#>>> 23
#print greatest([])
#>>> 0

    

Create 02.py