I never called the function, but stuff is printing anyway

#1

shopping_list = [“banana”, “orange”, “apple”]

stock = {
“banana”: 6,
“apple”: 0,
“orange”: 32,
“pear”: 15
}

prices = {
“banana”: 4,
“apple”: 2,
“orange”: 1.5,
“pear”: 3
}

Write your code below

We want to be sure the items we want are actually in stock. We won’t pay for what they don’t have.

def compute_bill(food):
total = 0
for item in food:
if stock[item] > 0:
total += prices[item]

else:
  print "no %s left" % item

return total

So, as you can see from the above, the only print command is in the function compute_bill(food). I define the function, but I don’t call it at any point. Yet when I click Run, the console prints out “no apple left” between one and four times.

#2 
shopping_list = ["banana", "orange", "apple"]

stock = {
  "banana": 6,
  "apple": 0,
  "orange": 32,
  "pear": 15
}
    
prices = {
  "banana": 4,
  "apple": 2,
  "orange": 1.5,
  "pear": 3
}

# Write your code below
# We want to be sure the items we want are actually in stock.  We won't pay for what they don't have.
def compute_bill(food):
  total = 0
  for item in food:
    if stock[item] > 0:
      total += prices[item]
      
    else:
      print "no %s left" % item
  return total
#3

That code is not asked for in the instructions, so should probably be removed. It is printing because the SCT may be calling the function to test it.

#4

Fair enough. So you’re saying it wouldn’t print anything if this was just a normal program instead of a teaching exercise that’s being graded by another program?

#5

The print statement is inside the function, so, yes, that’s it. There is no way for it to execute if the function is not called.

As for having the function print anythng, in my view that needs a rethink. When we look at the return statement it is a value (total). The operations of the function are essentially pure and only read values from the dictionaries as directed by the food list which computed values are accumulated to total.

In other words, a slightly more sophisticated approach would be needed to add verbosity to the outputs. For now, all we will want to print is the total that is returned.

print (compute_bill(shopping_list))

As a general rule, functions should be free of print statements and just do what they are intended to do, and return as needed. Then print.

Let’s play around with this function a wee bit. When you complete the unit on Advanced topics it will make sense, so put this aside until then. It merely demonstrates the added logic we can use to handle output and leave functions to do their special job.

stock = {
  "banana": 6,
  "apple": 0,
  "orange": 32,
  "pear": 15
}   
prices = {
  "banana": 4,
  "apple": 2,
  "orange": 1.5,
  "pear": 3
}

def back_order(s):
    return '\n'.join(['%s not served' % x for x in s]) if len(s) else None

def compute_bill(food):
    total = 0
    not_served = []
    for item in food:
        if stock[item] > 0:
            total += prices[item]
        else:
            not_served += [item]
    return (total, not_served)

shopping_list = ["banana", "orange", "apple"]

# unpack the call returns

total, not_served = compute_bill(shopping_list)

print ('Total: %.2f \n%s' % (total, back_order(not_served)))

Total: 5.50 
apple not served
#6

Ok, thanks. I’ll certainly come back and have a look at this when I’m done with that unit. I appreciate you taking your time to help me out with this.

#7

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