Identifiers in Python: Naming Rules & Best Practices

In Python, an identifier is simply a name used to identify a variable, function, class, or other object. Identifiers matter because they help your code stay organized, readable, and error-free. Using clear and meaningful names allows both you and others to understand the purpose of each element at a glance. 

This article will dive into what is an identifier in Python, explaining what they are, how to use them correctly, and why choosing the right names can improve your code’s overall quality. 

What are Identifiers in Python?

Different programming elements need to be identified and named uniquely to differentiate them from others of the same kind. These are referred to as Identifiers. The user defines these names according to their choice and requirements, including names for classes, functions, variables, methods, and more.

To understand what is an identifier in Python,  follow similar principles but also adhere to specific naming conventions unique to the language. Understanding what are identifiers in Python is essential for writing clean and efficient code. These must begin with a letter (A-Z or a-z) or an underscore (_) and can be followed by letters, digits (0-9), or underscores. However, they cannot be Python keywords or contain special characters like @, #, or $.

The importance of Python identifiers goes beyond just naming conventions—it’s about how they structure your code and help manage different components of your program. Here are three programs that can help you:

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Reserved words in Python which cannot be used as an identifier like function names or variable names are known as keywords. They are helpful in the definition of the structure and syntax of Python. As of Python 3.7, there are 33 keywords. This number may increase or decrease over time. Except ‘True’, ‘False’, and ‘None’, all other keywords are found in lowercase and need to be used accordingly, keeping the case sensitivity in mind. 

Here's an example to showcase how you can use identifiers in Python:

# Defining identifiers
student_name = "Ravi Kumar"
student_age = 21
student_city = "Delhi"

# Using identifiers
print("Student Name:", student_name)
print("Student Age:", student_age)
print("Student City:", student_city)

Output:

Student Name: Ravi Kumar

Student Age: 21

Student City: Delhi

Explanation:

• student_name, student_age, and student_city are all identifiers in Python. They represent different pieces of information about the student.
• These Python identifiers are valid because they follow the language’s naming rules: they start with a letter and contain only letters, digits, or underscores.
• The variables are used in the print() statements to output the values associated with them.

Python Identifier Naming Rules

When working with Python identifiers, it's crucial to follow the Python identifier rules to ensure your code runs smoothly and is easy to understand. These rules exist to prevent errors and maintain clarity, making it easier for developers to read and maintain code. 

For example, a rule like "identifiers must not start with a number" helps avoid ambiguity. If 1var were allowed as an identifier, it could confuse the interpreter and make the code harder to debug. 

Following Python identifier rules ensures your code is both functional and readable.

• Identifier names in Python can contain numbers (0-9), uppercase letters (A-Z), lowercase letters (a-z), and underscore (_).  
• The name should always start with a non-numeric character.
• An identifier name should not contain numeric characters only.
• Identifier names in Python are case-sensitive like most other languages. (‘Ash’ is different from ‘ASH’).
• Users can begin identifiers with an underscore; it will not display an error.
• An identifier name can be of any length, although the PEP-8 standard rule advises limiting the number of characters in a line to 79.
• Identifiers should not carry the same name as keywords. (To avoid errors in this regard, users can type help() followed by “keywords” to view a list of all the keywords in Python.)
• Leading double underscores (__$) cannot be used as these category names are used for the context of the definition of a class. These are private variables of derived and base classes. 

Deviation from any of these Python identifier rules  mentioned above may lead to error reports and cause runtime issues in the program:

By understanding and following the Python identifier rules, you set a strong foundation for writing clean, efficient code. These rules help you avoid mistakes and ensure that your code is both functional and readable. Now, let’s dive into valid and invalid identifiers in Python to see how these rules apply in real-world scenarios and to avoid common pitfalls.

Valid vs Invalid Python Identifiers (With Examples)

When working with identifiers in Python, it's important to understand the difference between valid and invalid identifiers in Python. A valid identifier in Python follows the rules and conventions set by the language, while an invalid identifier in Python breaks those rules. 

To understand what is an identifier in Python, these are simply names used to identify variables, functions, classes, and other objects. You’ll use Python identifiers frequently in your programs, so understanding how to create valid ones is essential.

Now let’s explore examples of valid and invalid identifiers in Python.

Valid Identifiers:

# Valid Python identifiers
student_name = "Aarav Sharma"
user_age = 22
total_sales = 25000
_employee_id = "EMP1234"

# Using valid identifiers
print("Student Name:", student_name)
print("User Age:", user_age)
print("Total Sales:", total_sales)
print("Employee ID:", _employee_id)

Output:

Student Name: Aarav Sharma

User Age: 22

Total Sales: 25000

Employee ID: EMP123450

Invalid Identifiers:

# Invalid Python identifiers
123var = 15  # Error: Starts with a digit
@username = "Rajesh"  # Error: Contains special character '@'
if = "Test"  # Error: 'if' is a reserved keyword
total-sales = 7000  # Error: Contains a hyphen '-'
user name = "Neha"  # Error: Contains a space

Explanation of the Difference:

• Valid Identifiers:
  • student_name, user_age, and total_sales are clear, readable identifiers that follow Python identifier rules. These names make the code easy to understand and maintain.
  • _employee_id is valid even though it starts with an underscore. This is a convention used to indicate that the variable is intended for internal or private use.
• Invalid Identifiers:
  • 123var is invalid because it starts with a digit. Python identifiers cannot begin with a number; they must start with a letter or an underscore.
  • @username is invalid because it contains the special character @, which is not allowed in Python identifiers.
  • if is a Python keyword, and keywords cannot be used as identifiers. Using them as identifiers will lead to a syntax error.
  • total-sales is invalid because it contains a hyphen (-). Python identifiers can only contain letters, digits, and underscores.
  • user name is invalid because it contains a space. Spaces are not allowed in Python identifiers; instead, underscores should be used to separate words (e.g., user_name).

Understanding valid and invalid identifiers in Python is essential for writing error-free Python code. Knowing what are identifiers in Python and following Python identifier rules will help you avoid common mistakes and follow best practices.

Also Read: Types of Data Structures in Python: List, Tuple, Sets & Dictionary

How to check Identifier Validity in Python? 

Python has a function which developers can use to check if an identifier name will be declared valid or not. It is the function identifier().

However, the limitation of this function is that it does not consider reserved keywords for identification.

To overcome this limitation, Python provides another function known as keyword identifier(). This function checks the validity of an identifier name while keeping the keywords in mind.

For example; 

print(“xyz”.isidentifier()) 

print(“88x”.isidentifier()) 

print(“_”.isidentifier())

print(“while”.isidentifier())

Output:

True

False

True

True (incorrect output)

There is another function str.isidentifier(), that can determine whether an identifier name is valid or not. 

Now that you understand the validity of Python identifiers, focus on applying these rules consistently in your code. Choose clear, descriptive names that align with best practices for Python identifiers. 

Keep improving your naming conventions, and always ensure your identifiers follow the rules to avoid common errors and enhance your code’s readability and maintainability.

Also Read: Java Identifiers: Definition, Syntax, & Best Practices 2025

Best Practices for Naming Identifiers

Although following Python’s rules is enough for generating unique identifier names which will be declared valid, professionally, users are suggested to follow a certain naming practice. This reduces minute, unforeseen problems and errors while experimenting with different types of identifier names. Even though these errors may seem negligible and might not report syntax errors initially, they can lead to runtime, or logical errors can occur, consequently displaying unwanted results. 

(For perspective, errors that occur in the code are known as syntax errors. When the syntax is correct, but the logic is wrong – ultimately leading the program towards a different path – the error is known as a runtime error.)

Here are the best practices for Python Identifiers:

1. For Naming Constants:

• Use all uppercase or capital letters for names.
• Users can separate words by an underscore. 
• Example: MAX_VALUE, SUMMATION_INDEX, etc.

2. For Package Names:

• Short names are preferred.
• Use of underscores is not advised.
• All characters should be in lowercase.
• Example: utilities, math, etc.

3. For Class Names 

• It is advised to start class names with uppercase letters. For example, Matrix, Transpose, Shuffle, etc. 
• For class names having multiple words, users can use capital letters for the starting alphabet of each word. For example, BubbleSort, ElectricBill, StandardData. 

Apart from this Following are the Best Naming Practices for Identifiers in Python

• If the identifier consists of two underscores, one at the beginning and one at the end, the identifier name is a language-defined special. Users should avoid this technique of naming.
• Generally, names of functions that return Boolean values begin with ‘is’. For example, isstring, iskeyword, etc.
• Identifier names can be of any length. But one should keep it short and precise for efficient usage. Like, First_inputed_value is acceptable, but it is better to use InpValue_1
• Identifier names should be kept meaningful for a better understanding of the program. To provide examples, ‘HRAvalue: conveys the underlying message better than ‘Asdf0022’.
• Technically, one can use underscores as the first and last characters, but it is advised not to do so because that format is used for Python built-in types.
• If the names of variables models for functions contain more than one word, then it is better to separate them with an underscore. Example: is_true(), Input_array(), object_inputted, etc. 
• Generally, module functions and variable names begin with lowercase alphabets. For example: dataentry(), pattern_1, etc. 

By following the best practices for Python identifiers, you can easily avoid common mistakes. Small errors like using reserved keywords or starting an identifier with a digit can lead to frustrating bugs. Staying mindful of naming conventions ensures your code remains clear and functional.

Also Read: Python Modules: Explore 20+ Essential Modules and Best Practices

Common Mistakes to Avoid

When working with Python identifiers, it's easy to make simple mistakes that can cause your code to fail or become hard to read. Here, we’ll highlight some of the most common mistakes to avoid, ensuring your code stays clean and error-free.

1. Using Python Keywords as Identifiers
   Python identifiers cannot be any of the reserved keywords like for, if, else, or class. Using them as identifiers in Python will result in a syntax error.
2. Starting Identifiers with Numbers
   Python identifiers must begin with a letter or an underscore, not a number. Using a number as the first character will cause the identifier to be invalid.
3. Using Special Characters
   Avoid using special characters like @, #, -, or spaces in your Python identifiers. These characters aren’t allowed and will make the identifier invalid.
4. Overusing Underscores
   While underscores are allowed, overusing them (e.g., my___var) can make your Python identifier harder to read. Keep it simple and clear.
5. Not Following Naming Conventions
   Not using clear, descriptive names for Python identifiers can make your code harder to understand. Stick to best practices for Python identifiers like using lower case with underscores for variables and upper case for constants.

Avoiding these common mistakes will help you use Python identifiers effectively and make your code more readable and less error-prone.

Understanding how to define identifiers in Python is key to writing clean, error-free code. By following the rules, avoiding common mistakes, and adhering to best practices, you'll make your code more efficient and easier to understand. With these tips, you’re now ready to confidently define identifiers in Python in your projects.  

Conclusion

Understanding what is identifier in Python is essential for writing efficient and error-free code.  As long as the naming rules are followed, these identifiers can be used without issues. However, to enhance readability and maintainability, it is advisable to follow universally accepted naming conventions.

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