Theisidentifier() method inPython is used to check whether a givenstring qualifies as a valid identifier according to the Python language rules. Identifiers are names used to identify variables, functions, classes, and other objects. A valid identifier must begin with a letter (A-Z or a-z) or an underscore (_), should contain only alphanumeric characters (A-Z, a-z, 0-9) and underscores (_), and should not be a reserved keyword in Python. In this article, we will see how theisidentifier() method works:

Let's understand with the help of an example:

s="variable_name"print(s.isidentifier())

True

Explanation:

• The string"variable_name" follows all the rules of a valid Python identifier:
  • It contains only letters, digits, and underscores.
  • It does not start with a digit.
  • It is not a Python keyword.
• Hence, the method returnsTrue.

Syntax of isidentifier()

string.isidentifier()

Parameters

• Theisidentifier() method does not take any parameters.

Return Type

• ReturnsTrue if the string is a valid identifier.
• ReturnsFalse otherwise.

Examples of isidentifier method()

1. Starting with a number

Anidentifier cannot start with a number.

# Starts with a numbers="1variable"print(s.isidentifier())

Explanation:

• The string"1variable" begins with the digit1, which violates the rules for identifiers.
• Consequently, the method returnsFalse.

2. Containing special characters

Special characters, apart from the underscore, are not allowed in identifiers.

s="var!name"# Contains a special character (!)print(s.isidentifier())

Explanation:

• The string"var!name" includes the special character!, making it an invalid identifier.
• The method appropriately returnsFalse.

3. Reserved keywords

Python’sreserved keywordscannot be used as identifiers. While they follow the naming rules, their special meaning in the language makes them invalid as identifiers:

s="class"# Reserved keyword in Pythonprint(s.isidentifier())

Explanation:

• The string"class" follows all identifier rules, soisidentifier() returnsTrue.
• However, using it as an identifier in code will lead to aSyntaxError because it is a reserved keyword.

4. Empty string

An empty string cannot qualify as an identifier:

s=""# Empty stringprint(s.isidentifier())

Explanation:

• The string is empty, so it cannot meet the rules for identifiers.
• The method returnsFalse accordingly.

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