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Python | Check if string is a valid identifier

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Identifier must begin either with the alphabet or with an underscore, it cannot start with a digit or any other special character, moreover, it can be followed by numbers.

 gfg: valid identifier 123: invalid identifier _abc12: valid identifier #abc: invalid identifier 

In this program, we use the search () method of the regex module. 
re.search (): this method either returns None (if the pattern does not match) or re.MatchObject which contains information about the matching part of the string. This method stops after the first match, so it’s better for checking regular expressions than for extracting data.

Let’s take a look at a Python program to determine if a string is an identifier or not.

# Python program to identify the identifier

 
# import re module

 
# re module provides support
# for regular expressions

import re

 
# Make a regular expression
# to identify a valid ID

< p> regex = ’^ [A-Za-z _] [A-Za- z0-9 _] * ’

  
# Define a function for
# define a valid ID

def check ( string): 

 

# pass a regular expression

# and a string in the search () method

if (re.search (regex , string)): 

print ( "Valid Identifier"

  

  else

print ( "Invalid Identifier"

 

 
Driver code

if __ name__ = = ’ __main__’

 

# Enter a string

string = "gfg"

 

  # run function call

check (string)

 

string = "123"

check (string)

 

string = "# abc"

check (string)

Output:

 Valid Identifier Invalid Identifier Invalid Identifier 

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