What is the string.isidentifier() method in Python?
The Python isidentifier() method checks if a string is a valid identifier or not.
Syntax
string.isidentifier()
Return value
The isidentifier() method returns True if the string is a valid identifier; otherwise, it returns False.
Rules for a valid identifier
In Python, a valid identifier should start with a letter in the alphabet (a-z or A-Z) or an underscore (_), followed by zero, more letters, numbers (0-9), or underscores. The identifier should not be a Python
isidentifier()doesn’t check if the string is a Python keyword. It only checks if the string starts with a letter or underscore, followed by letters, numbers, or underscores.
Examples of valid identifiers
-
one -
_two -
__three__ -
four_4
Examples of invalid identifiers
-
4four: Invalid because the identifier should start with a letter or underscore. -
fa＄: Invalid because the special character＄is used. -
continue: Invalid becausecontinueis a Python keyword.
Code example
identifier= "one"print(identifier, " isidentifier -- ", identifier.isidentifier())identifier= "4four"print(identifier, " isidentifier -- ", identifier.isidentifier())identifier= "continue"print(identifier, " isidentifier -- ", identifier.isidentifier())
Explanation
-
For the first string,
one, theisidentifier()method returnsTruebecause it is a valid identifier. -
For the second string,
4four, theisidentifier()method returnsFalsebecause it is not a valid identifier.
Identifiers should not start with numbers.
- For the third string,
continue,isidentifier()returnsTruebecause even though it is an invalid identifier, theisidentifiermethod doesn’t check for Python keywords.
How to check for keywords
To check if a string is not a keyword, we can use the iskeyword() method of the keyword module.
from keyword import iskeyword
print(iskeyword('continue')) # True
We can determine if a string is a valid identifier by checking if the string returns True for the isidentifier() method and False for the iskeyword() method.
from keyword import iskeyworddef is_valid_identifier(string):return string.isidentifier() and (not iskeyword(string))print(is_valid_identifier('continue'))print(is_valid_identifier('fa$'))print(is_valid_identifier('1fa'))print(is_valid_identifier('one_2_three'))print(is_valid_identifier('__'))