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Python Variable Naming Rules and Conventions

Learn Python variable name syntax, keywords, case sensitivity, snake_case, built-in shadowing, and practical valid-versus-invalid examples.

A variable name is an identifier: a name that lets your program refer to a stored value. In Python, assignment binds a name to a value with the = operator.

first_name = 'Tuna'
item_count = 3

In first_name = 'Tuna', first_name is the identifier, = is the assignment operator, and 'Tuna' is the value. The name can be used later to access that value.

Variable names follow syntax rules. Python also has naming conventions that make code easier to read and maintain. A convention is a recommendation, not a grammar requirement.

Python variable name rules at a glance

Allowed characters in identifiers

Ordinary Python variable names may contain alphabetic characters, digits, and underscores. An underscore is the character _; it is commonly used to separate words.

name_1 = 'Tuna'
user_age = 21
order_total_2026 = 49.95

Punctuation is not interchangeable with an underscore. For example, a semicolon cannot appear as part of an identifier. A hyphen is also not a valid name character because Python interprets it as the subtraction operator.

name;_1 = 'Tuna'  # SyntaxError
user-name = 'Tuna'  # SyntaxError: interpreted as user - name

The starting-character rule

A variable name must begin with a letter or an underscore. It must not begin with a digit. Digits are allowed after the first character.

name_1 = 'Tuna'   # valid
_name = 'Tuna'    # valid
name1 = 'Tuna'    # valid
1_name = 'Tuna'   # SyntaxError

Although a leading underscore is syntactically valid, names beginning with an underscore can have special conventions in larger programs. For ordinary beginner variables, a clear lowercase name such as user_name is usually easiest to understand.

Spaces and multiword names

Spaces cannot be part of one variable identifier. Python reads space-separated text as separate syntax elements, so first name is not one name. Python may interpret it as two expressions or report a syntax error when it appears in an assignment.

first name = 'Tuna'  # SyntaxError
first_name = 'Tuna'  # valid

Use snake_case for multiword names. Snake_case uses lowercase words joined by underscores, with no spaces.

Python keywords

A keyword is a reserved word with a special meaning in Python grammar. A keyword cannot be used as the target of an assignment.

class = 'Tuna'  # SyntaxError

Common keywords include if, class, for, while, def, return, True, False, and None. Choose an alternative such as class_name, item_count, or is_ready.

The exact keyword list depends on the Python version. Use the keyword module to inspect it:

import keyword
print(keyword.kwlist)

You can test whether a particular string is a keyword:

import keyword
print(keyword.iskeyword('class'))  # True
print(keyword.iskeyword('class_name'))  # False

Checking whether text can be an identifier

Strings have an isidentifier() method that checks whether their characters and starting character follow identifier rules.

print('first_name'.isidentifier())  # True
print('1_name'.isidentifier())      # False
print('first name'.isidentifier())  # False

isidentifier() is not a complete variable-name test because a keyword can have identifier-like characters. Check both conditions when needed:

import keyword

candidate = 'class'
valid_name = candidate.isidentifier() and not keyword.iskeyword(candidate)
print(valid_name)  # False

Built-in names and shadowing

A built-in is a name supplied by Python, such as print, list, str, id, type, or sum. Unlike keywords, built-in names are usually technically permitted as variable names.

Shadowing means assigning a new value to a name that Python would otherwise find in an outer scope or among the built-ins. The assignment below is accepted, but it hides the normal print() function:

print = 'Tuna'
print('Hello')  # TypeError: a string is not callable

The name print now refers to a string, not a function. Similar problems can result from assigning to list, str, id, type, or sum.

list = [1, 2, 3]
list('abc')  # TypeError, because list now refers to a list

Avoid these names for variables. If shadowing has already happened, rename the variable and restart the interpreter, or remove the name in an interactive session:

del print

first_name = 'Tuna'
First_Name = 'Salmon'

print(first_name)  # Tuna
print(First_Name)  # Salmon

first_name = 'Tuna'  # preferred
f_n = 'Tuna'          # less clear

first_name = 'Tuna'                    # concise and clear
first_name_of_a_person = 'Tuna'        # unnecessarily verbose

customer_name = 'Tuna'
def calculate_total(price, tax_rate):
    return price + price * tax_rate

MAX_RETRIES = 3
DEFAULT_TIMEOUT = 10

# Valid
name_1 = 'Tuna'
first_name = 'Tuna'
item_count2 = 2

# Invalid syntax
1_name = 'Tuna'
first name = 'Tuna'
class = 'Tuna'
user-name = 'Tuna'