Python updating a loop

Question

my program takes a mathematical input and checks it for errors before proceeding, here is the part of the code I need help with:

expression= introduction()#just asks user to input a math expression    
operators= set("*/+-")
numbers= set("0123456789")
for i in expression:
    while i not in numbers and i not in operators:
        print("Please enter valid inputs, please try again.")
        expression= introduction()

Now I have set up an error loop but the problem I am having is that I don't know what to update the loop with in this scenario. Anyone?

I need something simple such as the "while True" code in the answers below. The rest are too advanced. I need something close to the code that is posted in this OP.

Alok Singhal · Accepted Answer · 2012-11-07 23:32:36Z

3

I would do it something like this:

valid = operators | numbers
while True:
    expression = introduction()
    if set(expression) - valid:
        print 'not a valid expression, try again'
    else: 
        break

You only want to call introduction() once per bad expression. The way you do it now, you are calling introduction() for every invalid character in expression.

answered Nov 7, 2012 at 23:32

Alok Singhal

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1 Comment

Tim Pietzcker Over a year ago

@user1716168: This is a lot more simple than your code, and it's the correct way to handle this problem.

Tyler Crompton · Accepted Answer · 2012-11-08 16:42:53Z

1

expression = introduction()    
operators = {'*', '/', '+', '-'}
while any(not char.isnumeric() and char not in operators for char in expression):
    print("Please enter valid inputs, please try again.")
    expression = introduction()

edited Nov 8, 2012 at 16:42

answered Nov 7, 2012 at 23:33

Tyler Crompton

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3 Comments

SeesSound Over a year ago

I cannot utilize "import", "any", and "char" commands. I am limited to lists, and string manipulators, and the other most basic stuff. The other guy's way works... At least for operator input but not for numeric input...

Tim Pietzcker Over a year ago

any is a built-in function. Why can't you use it? Also, char is just a variable name, not a command.

Tyler Crompton Over a year ago

@user1716168, as Tim pointed out, any is a builtin function. I don't understand why you can't use that (unless you are modifying its value for some weird reason). Anyway, I simplified the code a bit.

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