How to check user input (Python)

Question

I have seen many answers to this question but am looking for something very specific. What I need to accomplish (in pseudo code) is this:

> FOR every ITEM in DICTIONARY, DO:
>           PROMPT user for input
>           IF input is integer
>                 SET unique-variable to user input

I'm very new to Python so the code may not be proper, but here is what I have:

def enter_quantity():
  for q in menu:
      quantities[q] = int(input("How many orders of " + str(q) + "?: "))

So this does everything but evaluate the user input. The problem I'm having is if the input is incorrect, I need to re-prompt them for the same item in the top-level for loop. So if it's asking "How many slices of pizza?" and the user inputs "ten", I want it to say "Sorry that's not a number" and return to the prompt again of "How many slices of pizza?".

Any/all ideas are appreciated. Thanks!

My final solution:

def enter_quantity():
for q in menu:
    booltest = False
    while booltest == False:
        inp = input("How many orders of " + str(q) + "?: ")
        try:
            int(inp)
            booltest = True
        except ValueError:
            print (inp + " is not a number. Please enter a nermic quantity.")
    quantities[q] = int(inp)

Padraic Cunningham · Accepted Answer · 2015-01-16 22:56:38Z

2

You need a while loop with a try/except to verify the input:

def enter_quantity():
    for q in menu:
        while True:
            inp = input("How many orders of {} ?: ".format(q))
            try:
               inp = int(inp) # try cast to int
               break
            except ValueError:
                # if we get here user entered invalid input so print message and ask again
                print("{} is not a number".format(inp))
                continue
        # out of while so inp is good, update dict
        quantities[q] = inp

edited Jan 16, 2015 at 22:56

answered Jan 16, 2015 at 22:45

Padraic Cunningham

181k30 gold badges264 silver badges327 bronze badges

Sign up to request clarification or add additional context in comments.

4 Comments

Ryan Over a year ago

Sorry! I omitted a piece of code... first post, I'll edit it to reflect that there was a FOR loop there. Thanks for your comment, I will try it out.

Padraic Cunningham Over a year ago

No prob, the main thing to take from the example is how to use a while loop with a try/except to verify the input. I updated my example

Ryan Over a year ago

Awesome. I figured out my solution and am going to mark your answer and show my code. Really appreciate the second set of eyes! Learning Python has been a lot of fun so far.

Padraic Cunningham Over a year ago

No prob, just so you know my code does what yours does we only leave the while each iteration when we get valid input

Snerx · Accepted Answer · 2018-11-15 11:40:39Z

This bit of code is a little more useful if a menu is added otherwise it crashes at the first hurdle. I also added a dictionary to store the input values.

menu = 'pizza', 'pasta', 'vino'
quantities = {}
def enter_quantity():

    for q in menu:
        while True:
            if q == 'pizza':
                inp = input(f"How many slices of {q} ?: ")
            elif q == 'pasta':
                inp = input(f"How many plates of {q} ?: ")
            elif q == 'vino':
                inp = input(f"How many glasses of {q} ?: ")
            try:
               inp = int(inp) # try cast to int
               break
            except ValueError:
                # exception is triggered if invalid input is entered. Print message and ask again
                print("{} is not a number".format(inp))
                continue
        # while loop is OK, update the dictionary
        quantities[q] = inp

    print(quantities)

Then run the code from this command:

enter_quantity()

Collectives™ on Stack Overflow

How to check user input (Python)

2 Answers 2

4 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

4 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related