Python infinite while loop issue

Question

I am trying to make a script that asks for user input in Python, it is supposed to error with the response "Please enter first name", and then return the user back to the initial input question prompt.

This isn't working, instead after asking for both the first and last name if no name is given for both I am thrown into an infinite loop of the first error.


# User input for first name
first_name = input('Enter FIRST name here: ')
# User input for last name
last_name = input('Enter LAST name here: ')

def print_name():

    # store user input in separate variable
    fname = first_name
    lname= last_name

    while True:
        # throw error if user enters no first name
        if len(fname) == 0:
            # error msg
            print('No FIRST name entered...')
            # loop back to prompt asking for first name
            continue
        else:
            # if first name given move on to prompting for last name
            # break loop
            break

    # loop into prompting user for last name
    while True:
        # throw error if user enters no last name
        if len(lname) == 0:
            print('No LAST name entered...')
            # loop back to prompt asking for last name
            continue
        else:
            # if last name given move on to running print command
            # break loop
            break

        return fname, lname

    print(f'your name is {fname} {lname}')

print_name()

Please can someone help me understand whats going wrong here? It should only loop back to asking for a first name (or last name) when nothing is given, other wise it should print the users name to console. both names should be given too, if first name is not given then id expect an error in the first while loop, like wise if last name is not given.

Also is there a better way to do this? using 2 while loops seems wrong?

You enter an infinite loop because len(fname) never changes. You need to ask for input again, this time storing it as fname. — mapf
– mapf, Commented May 4, 2020 at 11:39
How about you write a function that will loop until it gets a nonempty string from the user, and then returns it? Then you can call it twice to get the two names. — khelwood
– khelwood, Commented May 4, 2020 at 11:39

Tomalak · Accepted Answer · 2020-05-04 11:43:41Z

3

Don't repeat yourself. If you copy and paste a section of code, stop and think. It should either be a function, or a loop.

def wait_for_input(prompt):
    data = ""
    while data == "":
        data = input(prompt).strip()
    return data


def print_name(fname, lname):
    print(f'your name is {fname} {lname}')


first_name = wait_for_input('Enter FIRST name: ')
last_name = wait_for_input('Enter LAST name: ')

print_name(first_name, last_name)

Also, don't use comments to repeat what the code says.

answered May 4, 2020 at 11:43

Tomalak

339k68 gold badges547 silver badges635 bronze badges

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

1 Comment

Nav Over a year ago

This is something like what I was trying before using different functions to do different things but it got way more messy for me and I gave up haha. Yes you solution works a treat, it doesn't spit an error back to the user but this is actually better as they cant move forward until giving something. Perfect Thank you, and I understand it :)

RMPR · Accepted Answer · 2020-05-04 11:40:50Z

2

The issue is with your infinite loops, you can simplify your function like:

def print_name():
    first_name = ""
    last_name = ""
    # User input for first name
    while first_name == "":
        first_name = input('Enter FIRST name here: ')
    # User input for last name
    while last_name == "":
        last_name = input('Enter LAST name here: ')
    print(f'your name is {first_name} {last_name}')

answered May 4, 2020 at 11:40

RMPR

3,5314 gold badges22 silver badges33 bronze badges

Comments

Dominique · Accepted Answer · 2020-05-04 11:45:08Z

1

I have the impression you are new at this:

While-loops generally look as follows:

while <condition>
...
<check_condition>
...

This means that in most cases, at every time the loop is executed, the condition is re-calculated and checked again by the while.

In your case, this would become something like:

while (len(fname) == 0)
<show_error_message>
<get fname again>

The case you have written here (while true) also exists and is used regularly, but in very different cases, like in multi-threaded event-based programs:

while true
<get_event>

This means that a part of the program (a so-called thread) is waiting for an event (like a buttonclick) to be catched and then something happens. This, however, is mostly done in multi-threaded applications, which means that the "main" program is doing something, while a subprogram is handling the events, which are coming in.

answered May 4, 2020 at 11:45

Dominique

17.6k20 gold badges81 silver badges161 bronze badges

1 Comment

Nav Over a year ago

I am sort of new to it yes. thank you for this its good to know.

Ferran Marin · Accepted Answer · 2020-05-04 11:59:22Z

1

I am not fully understanding why you need so many loops. Something like this should do:

def print_name():
    fname = input('Enter FIRST name here: ')
    if len(fname) == 0:
        raise Exception('No FIRST name entered...')

    lname= input('Enter LAST name here: ')
    if len(lname) == 0:
        raise Exception('No LAST name entered...')

    print(f"your name is {fname} {lname}")

And if all you wanted is to repeat this loop all you need to do is nest your print_name() function in a loop.

EDIT: Now that I seen other answers, I believe @Tomalak answer is better, was not getting what you really wanted.

edited May 4, 2020 at 11:59

answered May 4, 2020 at 11:56

Ferran Marin

133 bronze badges

3 Comments

Nav Over a year ago

I am not an expert, I know there is a better way to do this and not have so many loops I just didn't know how I was trying to maintain DRY code but ended up with more issues so gave up. i was not aware of the "raise Exception" part of code. Thank you

Nav Over a year ago

This also works but does not loop the user back to the initial question on exception it just ends the script, this is why I thought a while loop would be included.

Ferran Marin Over a year ago

Yes, that is why I think Tomalak's answer is better, I did not take re-asking the user for the information into account.

Sanjit · Accepted Answer · 2020-05-04 11:53:49Z

Try this code:

def print_name():

    # store user input in separate variable
    first_name = input('Enter FIRST name here: ')

    fname = first_name



    while True:
        fname = first_name


        # throw error if user enters no first name
        if len(fname) == 0:
            # error msg
            print('No FIRST name entered...')
            first_name = input('Enter FIRST name here: ') 
            # loop back to prompt asking for first name
            continue
        else:
            # if first name given move on to prompting for last name
            # break loop
            break

    # loop into prompting user for last name
    while True:
        last_name = input('Enter LAST name here: ')
        lname= last_name

        # throw error if user enters no last name
        if len(lname) == 0:
            print('No LAST name entered...')
            # loop back to prompt asking for last name
            continue
        else:
            # if last name given move on to running print command
            # break loop
            break

        return fname, lname

    print(f'your name is {fname} {lname}')

print_name()

Collectives™ on Stack Overflow

Python infinite while loop issue

5 Answers 5

1 Comment

Comments

1 Comment

3 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

5 Answers 5

1 Comment

Comments

1 Comment

3 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related