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Python Python Basics (Retired) Shopping List Shopping List Project

Posted by Yukiru Kannazuki
Yukiru Kannazuki
3,036 Points

How do I assign a comma to each item in the Shopping List exercise, but add a period to the last one?

In Python's Shopping List exercise, Kenny challenges us to add a comma to the end of each item in the list, and I wanted to do something like: for item in shopping_list: while True:

  if shopping_list[last]:
    print(item + ". ")
    break

  for item in shopping_list:
  print(item + ", ")
    continue

I don't quite know, it still boggles my head. XD

3 Answers

Robert Richey
Robert Richey
Courses Plus Student 16,352 Points

Hi Oak,

This is definitely a brain twister. I'll show you two ways .

# First, the hard way. Let's use a for loop to print each item
# with proper punctuation, in one line

for item in shopping_list:
  if item == shopping_list[-1]:
    print(item + '.')
  else:
    print(item + ',', end=" ")

# type help(print) to see more about the arguments into the print function
# if confused about the end keyword argument

# Next, the easy way. We can do this in just one line.

print(', '.join(shopping_list) + '.')

The output from both ways is identical.

Hope this helps,

Cheers

Yukiru Kannazuki
Yukiru Kannazuki
3,036 Points

Thanks, it was a little off from what I was thinking, but it does get what needs to be done, done. Could you explain why shopping_list[-1] works as the last index, and what end=" " does?

Robert Richey
Robert Richey
Courses Plus Student 16,352 Points

Many videos ahead of where you are, Slicing With A Step briefly explains that lists can be indexed with negative values - at about the 3:58 mark. Basically, it allows you to index into the list from the end.

string = "Hello"

string[-1] == 'o'
string[-5] == 'H'

The end keyword argument in the print function tells print what to print out last. By default, this is a new line character, but we can change this to any character we want. In this case, I changed it to a space, which allowed it to print several consecutive words on the same line.

# If we used end="!", then

print("Hello World", end="!")

# will output: Hello World!
# and any additional output will begin immediately after the exclamation mark

Hope this helps,

Cheers

helmi al kindy
helmi al kindy
1,371 Points
helmi al kindy
helmi al kindy
1,371 Points

Hi Robert, I did your easier method of adding comas and a dot at the end. The problem is that it prints out the list the amount of times I have added to the list instead of once. Eg: if I add 4 items to the list it will print the list 4 times instead of 1. How do I make the list print only once with the comas and dot at the end ?

Robert Richey
Robert Richey
Courses Plus Student 16,352 Points

Hi Helmi,

It sounds like you may have print(', '.join(shopping_list) + '.') inside a loop. If it's not in a loop, I'll need to see your code to try and figure out what's happening.

Cheers

helmi al kindy
helmi al kindy
1,371 Points
helmi al kindy
helmi al kindy
1,371 Points

Hi Robert, Here is the code 

shopping_list = list()

print("What would you like to pick up at the store ? ")
print("Enter 'DONE' to stop adding items to the list. ")

while True:
  new_item = input("> ")

  if new_item == 'DONE':
    break

  shopping_list.append(new_item)
  print("Added! List has {} items.".format(len(shopping_list)))
  continue

print("Here's your list: ")

for item in shopping_list:
  print(', '.join(shopping_list) + '.')
Robert Richey
Robert Richey
Courses Plus Student 16,352 Points

The join() method acts on a list of values and returns a string containing all items, each separated by the given separator - in this case, the separator is the string value of a comma followed by a space.

# change this
for item in shopping_list:
  print(', '.join(shopping_list) + '.')

# to this
print(', '.join(shopping_list) + '.')

# For example
print(', '.join(['apple', 'peach', 'tomato']) + '.')

# Will output: apple, peach, tomato.
# No need to use a loop here

Hope this helps!

Cheers

helmi al kindy
helmi al kindy
1,371 Points
helmi al kindy
helmi al kindy
1,371 Points

Thanks Robert it worked well.