Python String isidentifier() Function

The String isidentifier() method returns True if the string is a valid identifier according to the language definition. Otherwise, it returns False.

note

A valid identifier can only have alphanumeric characters a-z, A-Z, 0-9 and underscore _ . The first character of an identifier can not be a digit. Also, identifier should not match a Python keyword (because it is a reserved identifier).

Syntax

my_string.isidentifier()

isidentifier() Parameters

Python String isidentifier() function does not take any parameters.

isidentifier() Return Value

Python String isidentifier() function returns:

• True if the string is a valid identifier.
• False if the string is not a valid identifier.

Examples

Example 1: Check if a String is an identifier with isidentifier()

The isidentifier() method returns True if the string is a valid identifier.

my_str = 'myIdentifier'
result = my_str.isidentifier()
print(result) # Output: True

output

True

An identifier can contain an underscore but not a special character.

my_str1 = 'my_identifier'
my_str2 = 'my identifier'
my_str3 = 'my-identifier'

print(my_str1.isidentifier()) # Output: True
print(my_str2.isidentifier()) # Output: False
print(my_str3.isidentifier()) # Output: False

output

True
False
False

An identifier can contain a digit, except for the first character.

my_str1 = '123myIdentifier'
my_str2 = 'myIdentifier123'

print(my_str1.isidentifier()) # Output: False
print(my_str2.isidentifier()) # Output: True

output

False
True

Example 2: Check if a Python Keyword is an identifier with isidentifier()

The isidentifier() method returns True for a string that matches a Python keyword, even though it is not a valid identifier.

print('class'.isidentifier()) # Output: True

output

True

To test if a string matches a Python keyword, use keyword.iskeyword():

from keyword import iskeyword

print(iskeyword('class')) # Output: True

output

True

note

A string is considered a valid identifier if .isidentifier() returns True and iskeyword() returns False.

from keyword import iskeyword

my_str = "myidentifier"

if my_str.isidentifier() and not iskeyword(my_str):
    print(f"'{my_str}' is a valid identifier")
else:
    print(f"'{my_str}' is not a valid identifier")

output

'myidentifier' is a valid identifier