0

I have a piece of code that asks for an input. The input must not contain any numbers:

def main():

    invalid = []
    foo = ""


    foo = str(input("Enter a word: ") )

    invalid = ["1","2","3","4","5","6","7","8","9","0"]

    for eachInvalid in invalid:
        if eachInvalid in foo:
            print("Not a real word!")
            main()
        else:
            pass


main()

So far, it works but I am not proud of it. What would be the better way of doing this be? For example, a word does not contain things like ~@: so I would have to add those to that list. How would I avoid this but keep the code rather clean and readable?

Also, another error, if I run the code and type something in like hello, that is valid but if I type something invalid it takes me back to the start but when I type a valid word it still says invalid? For example:

Enter a word: hello
>>> ================================ RESTART ================================
>>> 
Enter a word: 123
Not a real word!
Enter a word: hello
Not a real word!

How would I fix this error and what would be the best way of looking for invalid characters in an input?

edit: nevermind, regular expression is fine.

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7
  • "I would like to avoid regular expression if possible" Why? Commented Feb 25, 2015 at 17:16
  • 3
    Regexes are actually the best and simplest way to achieve it. Commented Feb 25, 2015 at 17:17
  • I want to keep my code simple and not import too many modules however, if it is easier to be done in regular expression then that's ok. Commented Feb 25, 2015 at 17:17
  • 1
    if any(char.isdigit() for char in foo):? Also, have a look at stackoverflow.com/q/23294658/3001761 Commented Feb 25, 2015 at 17:21
  • Note too that you don't have to "initialise variables" in Python - the first assignments to invalid and foo are totally redundant. Commented Feb 25, 2015 at 17:28

3 Answers 3

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6

While a more complex validation is an appropriate use case for a regular expression, in this simple case there is a built in function isalpha() which checks whether a string only contains alphabetic characters.

foo.isalpha()

Returns True or False.

Note that in Python 3 this will deal with all unicode characters defined as "letters".

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1 Comment

Thanks. Exactly what I was looking for, even works for words with an umlaut, etc.
0

You could use a simpler method to test for a digit in the whole string, rather than testing each letter individually.

if any(x.isdigit() for x in foo):
        print("Invalid Word")
    else:
        print("valid word")
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Comments

-1

You could reverse the way you are doing, instead of having a list of invalids, it is better to have a list of valids. Then check every character of your string :

valids = ['a', 'b', 'c', 'd']
for letter in foo:
    if (not letter in valids):
            print("Not a real word!")

It is even easier with regex as it is easier to list all valids options :

import re
if (not re.match("^[a-zA-Z_ ]*$", foo)):
            print("Not a real word!")

The regex ^[a-zA-Z_ ]*$ meaning a word that contain only symbols in [a-zA-Z_ ]

If you want to stay with a list of invalids, use negated regular expression :

if (re.match("[^0-9@]", foo)):
            print("Not a real word!")

where [^0-9@] means anything but the characters defined between the brackets

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1 Comment

^[a-zA-Z_ ]*$ might be more clear if it includes \s instead of whitespace (though i think it should be excluded since it would mean more than 1 word is given). Also, [^0-9@] wouldn't work since it matches characters like ,.!?- etc.

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