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Regular expression

Posted on 2006-11-22
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Last Modified: 2012-06-27
Hi,
How do i find out if a string contains any non alpha numeric characters using regular expression, in python?

Thanks

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Question by:jyotishb
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2 Comments

LVL 14

Expert Comment

ID: 18000437
import re
def has_non_alpha_num(s):
return bool(re.search(r'[^a-zA-Z0-9]', s))

print has_non_alpha_num("123")  # Prints False
print has_non_alpha_num("abc")  # Prints False
print has_non_alpha_num("Hello!")  # Prints True
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LVL 29

Accepted Solution

pepr earned 1500 total points
ID: 18001177
Also, you can use r'\W' special pattern sequence to match non-alphanum and not underscore characters (shortcut for [^a-zA-Z0-9_]). The alphanum plus underscore character can be expressed as r'\w' (shortcut for [a-zA-Z0-9_]). Depending on whether locale is set or not, the sequences consider ASCII letters or also 8-bit and unicode letters.

However, you can use also the method of the built-in string type which will probably be more efficient and takes into account also the 8-bit characters and Unicode strings.

print not s.isalnum()

Library reference -- 3.6.1 String Methods says:

isalnum( )
Return true if all characters in the string are alphanumeric and there is at least one character, false otherwise.
For 8-bit strings, this method is locale-dependent.

isalpha( )
Return true if all characters in the string are alphabetic and there is at least one character, false otherwise.
For 8-bit strings, this method is locale-dependent.

isdigit( )
Return true if all characters in the string are digits and there is at least one character, false otherwise.
For 8-bit strings, this method is locale-dependent.

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