Ending a loop without going back to the start (Python)

Question

I am trying to create a continuous user input but do not want it to restart from the start if a wrong info is put in. For e.g.,

a = 1
while a ==1:
    Number = raw_input("Number: ")
    if len(Number) != 3:
        print "\n Error, please enter 4 digits \n"
    else:    
        Day = raw_input("Day: ")
        if not Day.isdigit():
            print "\n Error, please enter day in digits \n"

Here, if the person enters a non-4 digit for the first input, the loop will end and go back to the start again. However, if he gets to the second input and enters a non-digit string, the loop will also end and go back to the start. How do I get it to not go back to the start but ask for the Day again?

The condition of the loop a==1 never becomes false because a never changes. If you want to end the loop, change a. — DYZ
– DYZ, Commented Feb 22, 2018 at 7:28
The whole point of a loop is that it goes back to the start, that's why it's a loop.. perhaps you don't need a loop? Please clarify your question — shakedzy
– shakedzy, Commented Feb 22, 2018 at 7:28
I do not want to end the loop as I want the user to continue entering data and I have an option for the user to end the loop manually. Perhaps I should not use a loop and that is my question: any other options to do what I want? — TYL
– TYL, Commented Feb 22, 2018 at 7:40

th3g3ntl3m3n · Accepted Answer · 2018-02-22 07:49:59Z

3

def myMethod():
    a = 1
    while True:
        if a is 1 and len(raw_input("NUMBER: ")) is not 3:
            print "ERROR IS HERE IN NUMBER"
        else:
            a = 2
            if a is not 1 and raw_input("DAY: ").isdigit() is True:
                a = 1
            else:
                print "ERROR IS HERE IN DAY"
myMethod()

you can use this for your purpose. key thing is you need to maintain a key for checking if there is error in DAY or in NUMBER.

Please let me know if you need any other clarification. this will ask you DAY: and NUMBER: infinitely

answered Feb 22, 2018 at 7:49

th3g3ntl3m3n

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Comments

DDGG · Accepted Answer · 2018-02-22 07:44:00Z

2

You can simplify this by function:

def input_number(prompt, digits_num=0):
    while 1:
        s = raw_input(prompt)

        if not s.isdigit():
            print "\n Error, please input digits \n"
            continue

        if digits_num:
            if len(s) != digits_num:
                print "\n Error, please enter %d digits \n" % digits_num
                continue

        result = int(s)
        break

    return result


number = input_number("Number: ", 4)
day = input_number("Day: ")

print "\n number=%d, day=%d" % (number, day)

answered Feb 22, 2018 at 7:44

DDGG

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1 Comment

TYL Over a year ago

This works great. And I can use it for other user inputs. Thanks a lot.

Mushif Ali Nawaz · Accepted Answer · 2018-02-22 07:51:06Z

1

You need two separate while loops for that purpose. One for number and the other one for day. Here is the corrected code:

number = ""
day = ""

while True:
    number = raw_input("Number: ")
    if not number.isdigit() or len(number) != 4:
        print "Error, Please enter a 4 digit number \n"
    else:
        break


while True:
    day = raw_input("Day: ")
    if not day.isdigit():
        print "\n Error, please enter day in digits \n"
    else:
        break

print "Number: ", number
print "Day: ", day

edited Feb 22, 2018 at 7:51

answered Feb 22, 2018 at 7:42

Mushif Ali Nawaz

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Comments

Shasha99 · Accepted Answer · 2018-02-22 08:16:47Z

1

If you can use Python 3, Use Enum in such scenarios for a production level code. You can always manipulate the conditions according to your needs. Here we go :

from enum import Enum

class Status(Enum):
    START = 1
    ‎MIDDLE = 2
    ‎END = 3

state = Status.START

while state != Status.END:
    while state == Status.START:
    ‎    Number = input("Number:")
    ‎    if len(Number) != 3:
    ‎        print("Invalid Number !")
    ‎    else:
    ‎        state = Status.MIDDLE

    while state == Status.MIDDLE:
    ‎    Day = input("Day:")
    ‎    if not Day.isdigit():
    ‎        print("Invaid Day !")
    ‎    else:
    ‎        state = Status.END 
    ‎

edited Feb 22, 2018 at 8:16

answered Feb 22, 2018 at 8:10

Shasha99

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Comments

Rayadurai · Accepted Answer · 2018-02-22 07:44:07Z

-3

Raise Exception until valid input

a = 1
while a ==1:
    try:
        Number = input("Number: ")
        if len(Number) != 3:
            print("\n Error, please enter 4 digits \n")
            raise RuntimeError()
    except RuntimeError:
        continue
    break

edited Feb 22, 2018 at 7:44

answered Feb 22, 2018 at 7:37

Rayadurai

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2 Comments

DYZ Over a year ago

Please format your code appropriately and do not use exceptions where a simple assignment can do the job.

jsotola Over a year ago

replace the raise RuntimeError() with continue ... get rid of the try/except

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