Python While Loop Not Returning Desired Value

Question

Just recently started learning python and ran into a bit of an odd problem. I've created this function to ensure that the number entered by a user is larger than zero:

def numcheck(value,variable):

    while value <= 0:
        print('The' +str(variable) + 'must be greater than zero! ')
        value = float(input('Please enter a positive number for' +str(variable)+ \
                            'and press enter. '))
    return value

The function is used within a main function as follows:

def main():
    length = float(input('What is the length of the block of cheese? '))
    numcheck(length,' length of the block ' )

My problem is that the function successfully recognizes non-positive values, but when a new value is entered, the original number is still passed to the rest of the function. For example, if -10 is entered into length, I will be prompted to enter another value. If 15 is entered, the while loop will close but -10 will still pass from the function completely ruining the arithmetic that follows. I have spent several hours trying to remedy this with no success. I would appreciate any advice y'all have to offer. Thanks so much!

You return the new value, but never assign to the old variable. — internet_user
– internet_user, Commented Mar 1, 2018 at 21:29
please make sure that the while loop statement has the correct identation tab — enneppi
– enneppi, Commented Mar 1, 2018 at 21:30
Possible duplicate of Asking the user for input until they give a valid response — Mr. T
– Mr. T, Commented Mar 1, 2018 at 21:30
Yes, it's not a very good question. But does question downvoters really want a newbie asking his first question in SO to immediately lose all his rep ? Maybe we should leave him some time to get used to SO before excluding him ? — kriss
– kriss, Commented Mar 1, 2018 at 21:41
My apologies for the quality of the question. I've been frustrated on this for several hours and just needed some assistance. The problem was fixed thanks to kriss, should I delete the thread? Obviously very new to SO — Jordan Williard
– Jordan Williard, Commented Mar 1, 2018 at 22:03

kriss · Accepted Answer · 2018-03-01 21:36:08Z

3

Python is pass by value. That means that the value of the variables passed to a function will be copied. If you modify a parameter variable of a function, it won't be changed outside it.

You just have to return the new length at the end of the function and call like:

length = numcheck(length,' length of the block ')

That way, you'll store the result in the length variable.

It's also not a very good practice to do your input both inside and outside the function. Duplicating the call to input is not really a problem, but both calls should be inside the function, the current way is ugly. But that's not the problem here.

edited Mar 1, 2018 at 21:36

answered Mar 1, 2018 at 21:30

kriss

24.3k17 gold badges104 silver badges120 bronze badges

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

Collectives™ on Stack Overflow

Python While Loop Not Returning Desired Value

1 Answer 1

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related