Limiting raw_input in python

Question

How can I limit the amount of characters that a user will be able to type into raw_input? There is probably some easy solution to my problem, but I just can't figure it out.

possible duplicate of Limiting Python input strings to certain characters and lengths — Ruben Bermudez
– Ruben Bermudez, Commented Apr 6, 2014 at 20:14
You either want the duplicate posted by @Ruben or if you want to not allow an input to exceed 40 chars, then you'll need to look at counting it on a char by char basis, see: stackoverflow.com/questions/510357/… — Jon Clements
– Jon Clements, Commented Apr 6, 2014 at 20:18

Christian Tapia · Accepted Answer · 2014-04-06 20:15:00Z

5

A simple solution will be adding a significant message and then using slicing to get the first 40 characters:

some_var = raw_input("Input (no longer than 40 characters): ")[:40]

Another would be to check if the input length is valid or not:

some_var = raw_input("Input (no longer than 40 characters): ")

if len(some_var) < 40:
    # ...

Which should you choose? It depends in your implementation, if you want to accept the input but "truncate" it, use the first approach. If you want to validate first (if input has the correct length) use the second approach.

answered Apr 6, 2014 at 20:15

Christian Tapia

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2 Comments

Bryan Oakley Over a year ago

It shouldn't depend on the implementation, it should depend on which gives the better user experience

Christian Tapia Over a year ago

I mean, what depends on the implementation is the way he will handle the input. If OP wants to reprompt for input if it has more than 40 characters, use @bigblind or @ JoranBeasley approaches.

anon582847382 · Accepted Answer · 2014-04-06 20:18:35Z

2

try this:

while True:
    answer = raw_input("> ")
    if len(answer) < 40:
        break
    else:
        print("Your input should not be longer than 40 characters")

edited Apr 6, 2014 at 20:18

anon582847382

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answered Apr 6, 2014 at 20:18

bigblind

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1 Comment

bigblind Over a year ago

Thanks @Alex Thornton, we tried to make the same edit at the same time :p

Joran Beasley · Accepted Answer · 2014-04-06 20:21:13Z

1

I like to make a general purpose validator

def get_input(prompt,test,error="Invalid Input"):
    resp = None
    while True:
         reps = raw_input(prompt)
         if test(resp):
            break
         print(error)
    return resp

x= get_input("Enter a digit(0-9):",lambda x:x in list("1234567890"))
x = get_input("Enter a name(less than 40)",lambda x:len(x)<40,"Less than 40 please!")
x = get_input("Enter a positive integer",str.isdigit)

answered Apr 6, 2014 at 20:21

Joran Beasley

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