Making a simple program, how to I make it so blank/spaces input doesn't count/add to it

Question

I am making a simple program that creates a grocery list. Right now, I am having trouble with blank input being added to my list: when I hit enter with or without spaces, it adds the blank input as an item. Is there a simple way to prevent this?

e.g. something like this as a fault tolerance:

#Enter your item or command: 
#Shopping items cannot be blank.
#Enter your item or command: 
#Shopping list items cannot be blank.

Current code:

List = []

def Menu():
    print('Here is a list of options:', '\n P : Print the List',
          '\n C : Empty the List', '\n E : Exit',
          '\n R : Print this command list')
def add(item):
    List.append(item)
    print("{0} has been added to the list".format(item))

# Having trouble here: I need to make it check against empty spaces and
#   not add to the list
def listInput():
    item = input('Enter an item or command: ')
    print('You have {0} items on your list.'.format(len(List)))
    return item

def print():
    print('Your shopping list:')
    for i in List:
        print("  * {0}".format(i))

def clear():
    del List[:]
    print('All items removed from list.')
    print('You have 0 items on your list.')

def start():
    print('Welcome to the your Shopping List Program')

def end():
    print('Thank you for using your Shopping List Program.')


def main():
    start()
    Menu()
    item = listInput()
    while item != 'E':
        if item == 'P':
            Print()

        elif item == 'R':
            Menu()

        elif item == 'C':
            clear()

        else:
            add(item)
        item = listInput()
    end()

main()

I'm not familiar with python, but when I try to run this with python 2.7.10 it gives a syntax error- are you allowed to declare a function called `print`, which is a builtin? Or is that an error by OP? — Karl Reid, May 26 '17 at 18:04

score 1 · Answer 1 · answered May 26 '17 at 18:03

1

Put in a guard that waits for non-empty input. Here is a simple version:

def listInput():
    item = ""
    while item.strip() == "":
        item = input('Enter an item or command: ')
    print('You have {0} items on your list.'.format(len(List)))
    return item

answered May 26 '17 at 18:03

Prune

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What exactly is the use of the `.strip()`, it would work without it too no? – Girrafish May 26 '17 at 18:06
`while not item.strip()` is better – C8H10N4O2 May 26 '17 at 18:06
@TheGirrafish: strip allows for white space on the line. – Prune May 26 '17 at 18:17
@C8H10N4O2: that depends on coding style. For a beginner, the value check is easier to read. For many advanced folk, the *not* idiom is preferable. – Prune May 26 '17 at 18:18

score 1 · Answer 2 · answered May 26 '17 at 19:06

The other answers here do a good job of more directly answering your question, but I'd recommend a slight rewrite of a little more than just the immediate problem.

Here is your current main() definition:

def main():
    start()
    Menu()
    item = listInput()
    while item != 'E':
        if item == 'P':
            Print()

        elif item == 'R':
            Menu()

        elif item == 'C':
            clear()

        else:
            add(item)
        item = listInput()
    end()

Here is how I would recommend you rewrite it:

def main():
    start()
    Menu()

    item = None
    while item != 'E':

        print('You have {0} items on your list.'.format(len(List)))
        item = listInput()

        if item == 'P':
            Print()

        elif item == 'R':
            Menu()

        elif item == 'C':
            clear()

        elif item == 'E':
            end()

        elif item is not None:
            add(item)

        else:  # item is None  -- this last else and print are optional
            print('Shopping items cannot be blank.')

It should be pretty self explanatory as to what it does (add a comment if you need clarification!), but the point is that it's easier to follow what's happening when you read the code, and you also eliminate redundant lines like having item = listInput() twice.

This will of course require a slight rewrite of listInput() as well, but it also allows us a slightly more elegant way of solving your problem:

def listInput():
    item = input('Enter an item or command: ').strip()
    if not item:
        item = None
    return item

Again, please let me know if you have questions, as I think the code speaks for itself and is fairly self-explanatory!

score 0 · Answer 3 · answered May 26 '17 at 18:02

0

Only add the item if it is not an empty string (with spaces removed), to do this you'll need to remove the else:

elif item.strip() != '':
    add(item)

answered May 26 '17 at 18:02

Nick is tired

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score 0 · Answer 4 · answered May 26 '17 at 18:06

0

Here is one option:

def listInput():
    item = input('Enter an item or command: ')
    while not len(item):
        item = input('Shopping items cannot be blank. Enter your item or command: ')
    print('You have {0} items on your list.'.format(len(List)))
    return item

answered May 26 '17 at 18:06

Eric Garnick

1

`len()` in `while not len(item)` is unnecessary, as the empty string is considered false. For slightly more robustness, I'd recommend this: `while not item.strip()`, as this will prevent whitespace from being added too. In case you want to remove extra whitespace anyway, however, this might be even better: `item = input('Enter an item or command: ')` `while not item:` – B. Eckles May 26 '17 at 18:53

Making a simple program, how to I make it so blank/spaces input doesn't count/add to it

4 Answers4