How to check a string for a special character?

Question

I can only use a string in my program if it contains no special characters except underscore _. How can I check this?

I tried using unicodedata library. But the special characters just got replaced by standard characters.

score 53 · Accepted Answer · edited May 23 '17 at 10:31

53

You can use string.punctuation and any function like this

import string
invalidChars = set(string.punctuation.replace("_", ""))
if any(char in invalidChars for char in word):
    print "Invalid"
else:
    print "Valid"

With this line

invalidChars = set(string.punctuation.replace("_", ""))

we are preparing a list of punctuation characters which are not allowed. As you want _ to be allowed, we are removing _ from the list and preparing new set as invalidChars. Because lookups are faster in sets.

any function will return True if atleast one of the characters is in invalidChars.

Edit: As asked in the comments, this is the regular expression solution. Regular expression taken from https://stackoverflow.com/a/336220/1903116

word = "Welcome"
import re
print "Valid" if re.match("^[a-zA-Z0-9_]*$", word) else "Invalid"

edited May 23 '17 at 10:31

Community

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1

answered Nov 14 '13 at 05:55

thefourtheye

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How can we use regular expression for this same question?? sorry to bother yu... im jus a beginner.. – Chuvi Nov 14 '13 at 07:05
let us [continue this discussion in chat](http://chat.stackoverflow.com/rooms/41158/discussion-between-chuvi-and-thefourtheye) – Chuvi Nov 14 '13 at 07:24
2

@Awknewbie Include space also in the RegEx like this `"^[a-zA-Z0-9 _]*$"` – thefourtheye May 28 '17 at 03:20
Isn't the regex `[^a-zA-Z0-9_]*$` with the `^` inside the brackets? That's what worked for me – clabe45 Mar 20 '18 at 20:57

score 6 · Answer 2 · answered Nov 14 '13 at 06:25

6

You will need to define "special characters", but it's likely that for some string s you mean:

import re
if re.match(r'^\w+$', s):
    # s is good-to-go

answered Nov 14 '13 at 06:25

U2EF1

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Returns True for white space – Cybernetic Jul 12 '20 at 18:11

score 0 · Answer 3 · answered Jul 16 '20 at 18:50

0

Everyone else's method doesn't account for whitespaces. Obviously nobody really considers a whitespace a special character.

Use this method to detect special characters not including whitespaces:

import re

def detect_special_characer(pass_string): 
  regex= re.compile('[@_!#$%^&*()<>?/\|}{~:]') 
  if(regex.search(pass_string) == None): 
    res = False
  else: 
    res = True
  return(res)

answered Jul 16 '20 at 18:50

Cybernetic

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That regex cant find any occurance of [ and bunch of others – Diego Vinícius Nov 28 '20 at 18:04

score 0 · Answer 4 · answered Apr 01 '21 at 02:50

Like the method from Cybernetic, to get those extra characters missed, modify the 2nd line of the function from

regex= re.compile('[@_!#$%^&*()<>?/\|}{~:]')

to

regex= re.compile('[@_!#$%^&*()<>?/\\|}{~:\[\]]')

where the \ and ] characters are escaped with \

So in full:

import re

def detect_special_characer(pass_string): 
  regex= re.compile('[@_!#$%^&*()<>?/\\\|}{~:[\]]') 
  if(regex.search(pass_string) == None): 
    res = False
  else: 
    res = True
  return(res)

score 0 · Answer 5 · answered Jun 19 '21 at 17:04

0

If a character is not numeric, a space, or is A-Z, then it is special


for character in my_string
   if not (character.isnumeric() and character.isspace() and character.isalpha() and character != "_")
       print(" \(character)is special"

answered Jun 19 '21 at 17:04

some dude

11
2

How to check a string for a special character?

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