Identifiers in Python: Naming Rules & Best Practices
Updated on Jul 11, 2025 | 12 min read | 15.83K+ views
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Updated on Jul 11, 2025 | 12 min read | 15.83K+ views
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Did you know? Python identifiers can include Unicode characters-meaning you can name your variables in emojis or non-English scripts! This makes coding more expressive and inclusive worldwide |
Identifiers in Python are names used to identify variables, functions, classes, modules, and other objects. Python has specific naming rules that must be followed to ensure proper functionality, such as starting with a letter or underscore, followed by letters, numbers, or underscores.
In this blog, we will explore these naming rules in detail, along with best practices for creating clear, readable, and maintainable identifiers in Python. We’ll also highlight common mistakes to avoid when naming your Python identifiers.
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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:
Reserved words in Python, known as keywords, cannot be used as identifiers for functions or variables. They define Python's syntax and structure. As of Python 3.7, there are 33 keywords, a number that may change over time. Except for ‘True’, ‘False’, and ‘None’, all keywords are lowercase and must be used with 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:
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Now that we understand what identifiers are in Python, let's explore the rules that govern how they should be named.
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.
Deviation from any of these Python identifier rules mentioned above may lead to error reports and cause runtime issues in the program.
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Having covered the naming rules for Python identifiers, let's now look at some examples to distinguish between valid and invalid identifiers.
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.
Now let’s explore examples of valid and invalid identifiers in Python in the table below.
Identifier |
Valid/Invalid |
Reason |
my_var | Valid | Starts with a letter and contains only letters and underscores. |
var_123 | Valid | Starts with a letter and contains letters, digits, and an underscore. |
1var | Invalid | Starts with a digit, which breaks the rule for Python identifiers. |
class | Invalid | class is a reserved keyword in Python, so it cannot be used as an identifier in Python. |
MyVar | Valid | Starts with a letter and uses only letters, which is allowed. |
my-var | Invalid | Contains a hyphen, which is not allowed in Python identifiers. |
_my_var | Valid | Starts with an underscore, which is a valid option for Python identifiers. |
True | Invalid | True is a Python boolean value, not an allowed identifier 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
Explanation:
This code shows valid Python identifiers. Four variables are defined: student_name, user_age, total_sales, and _employee_id, each holding respective data. The print() function then displays the values of these variables. The identifiers follow Python's naming rules and store information about a student, their age, sales, and an employee ID.
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:
This code demonstrates invalid Python identifiers. Variables like 123var, @username, if, total-sales, and user name are invalid due to issues like starting with a digit, containing special characters, using reserved keywords, having a hyphen, or including spaces. These violate Python's naming rules and will result in errors.
Explanation of the Difference:
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.
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Now that we've seen examples of valid and invalid Python identifiers, let's explore how you can check the validity of an identifier 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.
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Having learned how to check the validity of identifiers in Python, let's now focus on the best practices for naming identifiers effectively.
Following Python’s rules ensures valid identifiers in Python, but using professional naming practices helps prevent subtle issues. While these errors may not cause syntax issues right away, they can lead to runtime or logical errors, producing unexpected results.
Syntax errors occur when the code violates rules, while runtime errors happen when incorrect logic alters the program’s flow.
Here are the best practices for Python Identifiers:
Constants should be easily distinguishable from variables, and naming them in all uppercase letters helps achieve this. It also makes constants more noticeable and easier to understand in code.
Package names should be short, simple, and clear. Using lowercase letters without underscores ensures consistency and better readability when importing packages.
Class names should begin with uppercase letters to differentiate them from other identifiers. For multi-word names, capitalize the first letter of each word to make the name more readable and structured.
Apart from this following are the best naming practices for identifiers in Python:
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Now that we've covered the best practices for naming identifiers, let's look at some common mistakes to avoid when working with them in Python.
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.
Avoiding these common mistakes will help you use Python identifiers effectively and make your code more readable and less error-prone.
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After reviewing the common mistakes to avoid, it’s important to understand the best practices for naming identifiers in Python. Learn how to do this effectively with upGrad.
Identifiers in Python follow specific naming rules that help ensure code clarity and prevent errors. By adhering to best practices, such as using uppercase for constants and following appropriate naming conventions for variables, functions, and classes, you can improve the readability and maintainability of your code.
upGrad offers tailored courses that teach Python programming and coding best practices. With hands-on projects and expert guidance, upGrad can help you learn identifiers in Python and other key concepts to advance your coding skills and career. Explore these courses to build your expertise:
You can also get started with free courses like:
To help bridge this gap, upGrad’s personalized career guidance can help you explore the right learning path based on your goals. You can also visit your nearest upGrad center and start hands-on training today!
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Pavan Vadapalli is the Director of Engineering , bringing over 18 years of experience in software engineering, technology leadership, and startup innovation. Holding a B.Tech and an MBA from the India...
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