# This module demonstrates Python exception handling
# An exception is a runtime error, often due to incorrect user input

# In the first example, we take a list that we assume to be a collection of numeric values representing
# ages of people and use it to compute an average age. We want to make sure that the program won't 
# crash if it encounters a non-numeric value. 

ages = [18, 20, 'fred', 23, 45] # our input list with a bad value ('fred') inside 
values = len(ages) # this will be the divisor we use to compute the average

sumAges = 0        # the running sum of ages in the list
for age in ages:   # for each age in the list,
	print age      # print it out
	try:
		sumAges += age # try incrementing sumAges by age
	except:
		# We get here if something goes wrong. We don't look for a specific error in this
		# example. With my data, adding 'fred' to a list of integers causes one. Therefore, we
		# end up here.
		print 'got a bad value, skipping ' + str(age)
		values -= 1 # decrement number of valid ages by 1

print 'the average age is ' + str(sumAges / float(values)) # watch out for integer division!!