Isidentifier method in String Python

In this Python tutorial, I will explain what is isidentifier method in string Python. We will see its syntax, Parameter, and return values, We will also see some use cases where the isidentifier() method in Python string can comes into use.

Python, one of the world’s most popular programming languages, is known for its extensive standard library and built-in methods to perform common tasks. Among these is the string isidentifier() method, a lesser-known but useful function in string manipulation and validation.

A string is a data type in Python programming that represents a sequence of characters, such as words or sentences. It can include letters, numbers, symbols, and spaces, and is typically enclosed in quotes (" " or ' ') in code

Introduction to the isidentifier() method in string Python

The string isidentifier method is a built-in string method in Python. It checks whether the given string is a valid identifier according to Python’s rules. Not all strings can serve as identifiers.

An identifier is essentially a name used to identify a variable, function, class, module, or other object. Identifiers in Python follow a certain set of rules and the Python isidentifier method checks these for us. This makes string isidentifier() a useful method for validating string names for this purpose.

Rules for a Valid Identifier

  • The identifier must start with a letter (a-z, A-Z) or an underscore (_).
  • The subsequent characters can be letters, underscores, or digits (0-9).
  • Identifiers cannot be Python-reserved words (like def, if, else, etc.).
  • An identifier cannot start with a number or whitespace.
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Use cases for the isidentifier method in string Python

There can be many different use cases for the string identifier() method in Python, some of them are listed:

  • Dynamic Code Generation
  • Config File Validation
  • Database Schema Validation
  • Ensuring Safe Script Execution

Let’s see them one by one with illustrative examples.

Case-1: Using the isidentifier in Python string method for dynamic code generation

If we’re writing a tool that generates Python code, we’d want to ensure the names being generated are valid identifiers.

For instance, when creating class or function names on-the-fly based on user input or data, we’d want to ensure the generated names are valid identifiers.

def generate_class_name(user_input):
    if user_input.isidentifier():
        return f"class {user_input}:\n    pass"
        return "Invalid class name!"

user_input = input("Enter a class name: ")

The Output is: let’s give two different inputs and see find what happens.

Enter a class name: Music
class Music:

Enter a class name: 1234
Invalid class name!
Python isidentifier method in string

This way we can use the isidentifier() function in Python string to identify the names of the user input.

Case-2: The isidentifier method in Python string for Config File Validation

For example, If we’re writing software that reads configurations from files or databases, we might want to check that keys (which might be used as attribute or variable names) are valid identifiers.

config_data = {
    "api_key": "12345",
    "timeout-value": 30,
    "default_user": "admin"

for key in config_data:
    if not key.isidentifier():
        print(f"'{key}' is not a valid identifier and might cause issues!")

The output is:

'timeout-value' is not a valid identifier and might cause issues!
isidentifier method in String Python

This we can give a warning using the str isidentifier Python method.

Case-3: String isidentifier() Python method for Database Schema Validation

Let’s create database schemas in Python based on user-defined input or from other non-standardized sources, checking column names or table names to ensure they are valid identifiers can be crucial.

table_columns = ["name", "age", "address-line1", "employee_id"]

for column in table_columns:
    if not column.isidentifier():
        print(f"'{column}' is not a valid identifier for a column name!")

The output is:

'address-line1' is not a valid identifier for a column name!
Python string isidentifier method

This way we can use the string Python isidentifier method in the database schema Validation.

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Case-4: Ensuring Safe Script Execution with the str.isidentifier() method in Python

If building tools that allow users to define scripts or routines, ensuring function or variable names are valid identifiers can prevent runtime errors.

def execute_user_script(variable_name, value):
    if variable_name.isidentifier():
        exec(f"{variable_name} = {value}")
        print(f"Assigned {value} to {variable_name} ,valid variable name!")
        print("Invalid variable name provided!")

execute_user_script("user_age", 25)
execute_user_script("user-age", 70)

The output is: Here, in the first case “user_age” is a valid identifier because it just contains alphabets and underscore. While in the second case “user-age” is not a valid identifier as it contains a “-” special character in it.

Assigned 25 to user_age ,valid variable name!
Invalid variable name provided!
isidentifier method in Str python

This way we can use the str.isidentifier method in Python for ensuring safe script execution.

Limitations of the isidentifier method in str Python

While str.isidentifier() is undeniable, and a helpful tool in validating Python identifiers, it’s essential to be aware of its limitations and the broader context of its use.

Only Checks Syntax, Not Semantics

str.isidentifier method in Python, checks if a string conforms to the syntax rules for Python identifiers. It does not, however, check the semantic meaning. This means while the method might confirm that a string can be used as an identifier, it doesn’t guarantee that it should be used as one.


"for".isidentifier() # Returns True

While “for” is a valid identifier by structure, it’s a reserved keyword in Python. Using it as a variable or function name would be a bad practice and lead to errors.

Doesn’t Check for Existing Names

The Python str isidentifier method does not check if the given identifier is already defined in the current scope or if it would overshadow a built-in name. Overwriting or shadowing existing names can introduce hard-to-trace bugs.

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list = [1, 2, 3] # Overwriting the built-in list type

Although the string “list” is a valid identifier, using it as a variable name like this would overwrite the built-in list type, leading to potential issues later in the code.

Unicode Considerations

Python 3 allows a wide range of Unicode characters to be used in identifiers. While this is a feature and not a limitation per se, it does mean that str.isidentifier() may return True for strings that look unusual as Python identifiers to many developers, especially those accustomed to ASCII-only names.


"π".isidentifier() # Returns True for Python 3

The Greek letter π is a valid identifier in Python 3. However, it might be confusing or seem non-standard to many developers.

Does Not Account for Stylistic Conventions

Python has well-established style guidelines (PEP 8) that provide conventions for naming variables, functions, classes, etc. While the Python str.isidentifier() method might affirm that a string is syntactically valid, it won’t tell us if it is stylistically recommended.


"myFunctionName".isidentifier() # Returns True

While “myFunctionName” is a valid identifier, according to PEP 8, function names should be lowercase with underscores (my_function_name), making it more Pythonic.


In this article, we have learned about what is isidentifier method in string Python. We have seen what is its syntax, parameters, return values, and limitations in detail. We have also seen what are the different use cases where we can use the str.isindentifier method with an illustrative example.

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