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Python Python Collections (Retired) Lists Redux Shopping List Take Three

Travis Jewell
Travis Jewell
10,381 Points
Posted by Travis Jewell
Travis Jewell
10,381 Points

Try Block - Continue with Index Input?

I want add the try block and if the exception occurs, have the program continue at the point where it asks the user to input the index. I've tried a bunch of different ways but I haven't been able to figure this out. The program always reverts back to the point where the user is asked to enter more shopping items. Is there a concise way to accomplish this?

shopping_list = []

def show_help():
    print("\nSeparate each item with a comma.")
    print("Type DONE to quit, SHOW to see the current list, and HELP to get this message.")

def show_list():
    count = 1
    for item in shopping_list:
        print("{}: {}".format(count, item))
        count += 1

print("Give me a list of things you wish to shop for.")
show_help()

while True:
    new_stuff = input("> ")

    if new_stuff == "DONE":
        print("\nHere is your list:")
        show_list()
        break
    elif new_stuff == "HELP":
        show_help()
        continue
    elif new_stuff == "SHOW":
        show_list()
        continue
    else:
        new_list = new_stuff.split(",")
        index = input("Currently {} items in the list.  Add this at a certain spot? "  
                      "Press enter for the end of the list, or give me a number: ".format(
                    len(shopping_list)))
        if index:
            while index:
                try:
                    spot = int(index) - 1
                    for item in new_list:
                        shopping_list.insert(spot, item.strip())
                        spot += 1
                    break
                except ValueError:
                    index = input("{} is not a number. Please try again. " 
                                    "\nEnter a valid number " 
                                  "or press enter for end of the list: ".format(index))
                    if index:
                        continue
                    else:
                        for item in new_list:
                            shopping_list.append(item.strip())
                        break
        else:
            for item in new_list:
                shopping_list.append(item.strip())

4 Answers

Steven Parker
Steven Parker
231,275 Points
Steven Parker
Steven Parker
231,275 Points

This code seems incomplete. There are some break and continue statements in it, but no visible loop. It would help to include the complete code. Or better yet, make a snapshot of the workspace and provide the link to it.

But the basic idea is you need a loop that begins right before where the user inputs the index and ends after the except block. In the except block you will continue, but when the try succeeds you will break out of the loop.

Travis Jewell
Travis Jewell
10,381 Points
Travis Jewell
Travis Jewell
10,381 Points

I figured it out. Thank you so much for your help!

Tessa Sullivan
Tessa Sullivan
1,517 Points
Tessa Sullivan
Tessa Sullivan
1,517 Points

I wanted to repeatedly ask the user for a number if they entered in anything but an integer or nothing (i.e., just hit enter). Here's how I did it:

if index:
  # Set the spot empty to trigger the while loop
  # while spot is not an integer, ask them to enter a valid number (or enter)
  spot = ''
  while type(spot) is not int:
    try:
      spot = int(index) - 1
    except ValueError:
      index = input("{} is not a number.  "
                  "Please re-enter the item number or press enter for end of list.".format(index))

    # If user hits 'enter', then we set spot to the end of the list and break out of the while loop
      if index == '':
        spot = len(shopping_list)
        break

  # Now we insert the items at the entered (or calculated) spot
  for item in new_list:
    shopping_list.insert(spot, item.strip())
    spot += 1

else: # if user did not enter a number, just append the new list to the end of the current list
  for item in new_list:
    shopping_list.append(item.strip())
Travis Jewell
Travis Jewell
10,381 Points
Travis Jewell
Travis Jewell
10,381 Points

Ok, I think I've got it all figured out now! If the user enters an invalid number, it asks for a valid number. If the user then enters a valid number, it will index accordingly, but if the user just presses enter, it will add the words to the end of the list.

If you notice any problems, let me know!

Timothy Recker
Timothy Recker
12,086 Points
Timothy Recker
Timothy Recker
12,086 Points

I struggled for a while trying to accomplish the same thing by myself. Looking at this thread and following Steven Parker's advice helped me, and I thought I'd go ahead and post the code I ended up with in case it would be helpful to someone else (note: the code I started with is a copy of Kenneth's, with the exception of some additional printed text and lines I added to make the feedback more appealing to me):

    else:
        new_list = new_stuff.split(",")
        while True:
            index = input("""
Add this at a certain spot? Press enter for the end of the list,
or give me a number. Currently {} items in the list.
> """.format(len(shopping_list)))
            if index:
                try:
                    spot = int(index) - 1
                    for item in new_list:
                        shopping_list.insert(spot, item.strip())
                        spot += 1
                    print("")
                    print("Item(s) added!")
                    print("")
                    break
                except ValueError:
                    print("")
                    print("{} is not a number. Please try again: ".format(index))
                    continue
            else:
                for item in new_list:
                    shopping_list.append(item.strip())
                print("")
                print("Item(s) added!")
                print("")
                break

Key additions include:

  1. a "while True:" loop in the line before "index = input(..."
  2. a "try:" in the line before "spot = int(index) - 1"
  3. an "except ValueError:" at the same indentations as the "try:" above that prints an error message
  4. "break" at the end of any successful input for index (i.e. an integer or an empty string)
  5. "continue" at the end of an invalid input for index (i.e. a non-integer)