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Python

Posted by Tayler Kemsley
Tayler Kemsley
21,479 Points

Can't get my while loop to stop looping!

Hi guys,

So I'm a beginner in Python, and I'm at the part of the lesson where you're asked to make a basic shopping list.

I thought I'd give it a try on my own before I tried the lesson to make sure I was getting a good idea of the language but am struggling. Here's my code so far:

shopping_list = []
finished = False

def add_item(item):
    if item.upper() == "DONE":
        print (shopping_list)
        finished = True
    elif item in shopping_list:
        print ("This item is already on your list")
    else:
        shopping_list.append(item)

while finished == False:
    add_item(input("What would you like to add?: "))

It works fine, but I can't get the loop to STOP looping. As you can see in the add_items function, the finished variable should change to True and stop the loop but it never does.

I figure I'll never learn if I don't ask so... here I am! Thanks in advance guys.

2 Answers

Haider Ali
seal-mask
.a{fill-rule:evenodd;}techdegree seal-36
Haider Ali
Python Development Techdegree Graduate 24,728 Points
Haider Ali
.a{fill-rule:evenodd;}techdegree seal-36
Haider Ali
Python Development Techdegree Graduate 24,728 Points

Hi Tayler, I have taken a look at your code and found that you have not used the global keyword inside your function. This is required if you want to change values of variables outside of the function. Inside your function, at the top, add global followed by the name of the variable you want to change. Your code should look like this:

shopping_list = []
finished = False

def add_item(item):
    global finished    #add this line in
    if item.upper() == "DONE":
        print (shopping_list)
        finished = True
    elif item in shopping_list:
        print ("This item is already on your list")
    else:
        shopping_list.append(item)

while finished == False:
    add_item(input("What would you like to add?: "))

This is something you may not have learned but it is needed to change variables which are outside the function.

Tayler Kemsley
Tayler Kemsley
21,479 Points

Ah that's interesting! Thanks so much.

So the "finished" variable inside the add_item function was ONLY inside that function.

I was probably jumping the gun, I'd wager the next video I watch will explain this!

Thanks again.

Chris Freeman
MOD
Chris Freeman
Treehouse Moderator 68,423 Points
Chris Freeman
Chris Freeman
Treehouse Moderator 68,423 Points

This a great question. It is important to know when a variable is referencing a local variable or a global (module) variable.

When referencing a variable, if not found in the local scope of a function, the next level up is checked for the variable. This continues until the module level.

The exception is when a variable is assigned, the variable becomes local. 

shopping_list = []
finished = False  # global finished

def add_item(item):
    if item.upper() == "DONE":
        print (shopping_list)
        finished = True. # local finished
    elif item in shopping_list:
        print ("This item is already on your list")
    else:
        shopping_list.append(item)

while finished == False:  # global finished
    add_item(input("What would you like to add?: "))

To make the finished inside of add_item behave as you wish, add a global statement:

def add_item(item):
    global finished
    if item.upper() == "DONE":
        print (shopping_list)
        finished = True. # global finished
    elif item in shopping_list:
        print ("This item is already on your list")
    else:
        shopping_list.append(item)