Variable Names

Variable names in Python are identifiers used to reference values stored in memory. Choosing good variable names is important for writing clear and maintainable code. Here are the key rules and best practices for naming variables in Python:

1. Variable Naming Rules

• Start with a letter or underscore (_): A variable name must begin with a letter (a-z, A-Z) or an underscore (_).
  • Example: my_var, _myVar, var1
• Case-sensitive: Variable names are case-sensitive, so myVar and myvar would be considered different variables.
• Letters, digits, and underscores only: After the first letter, variable names can include letters, numbers, and underscores but no spaces or special characters.
  • Example: total_sum, var123, price_in_usd
• No reserved keywords: You cannot use Python reserved keywords (such as for, if, while, return, etc.) as variable names.

2. Best Practices for Naming Variables

• Descriptive names: Use meaningful names that describe the purpose of the variable. This makes your code easier to understand.
  • Good example: student_count, total_price
  • Bad example: x, tmp, a1
• Use underscores for readability: For multi-word variable names, use underscores to separate words. This is known as snake_case.
  • Example: first_name, max_speed, user_id
• Avoid single-letter names: Unless for loop counters or very short-lived variables, avoid single-letter names.
  • Example: Use index instead of i, sum_of_values instead of s.
• Consistency: Be consistent with your naming convention throughout your code. Stick to either snake_case or camelCase, but avoid mixing them.
• Avoid starting with an underscore unless necessary: Names that begin with an underscore often have special meanings in Python (e.g., _single_leading_underscore indicates a weak "internal use" variable, __double_leading_underscore invokes name mangling).

3. Common Naming Conventions

• Snake_case: This is the most common naming convention in Python, especially for variables and functions.
  • Example: file_name, user_input
• CamelCase: Sometimes used in class names, where the first letter of each word is capitalized.
  • Example: MyClass, UserProfile

4. Examples of Good and Bad Variable Names

5. Avoiding Common Mistakes

• Don’t use names that are too similar to existing variables, as this can lead to confusion.
• Avoid using names that are too generic, like data, value, or info. Be as specific as possible.

6. Reserved Keywords

Python has a set of reserved keywords that you cannot use as variable names. Some of these include False, class, finally, is, return, None, continue, for, lambda, try, etc.

You can check the list of Python reserved keywords by importing the keyword module:

import keyword
print(keyword.kwlist)

Example

Here’s an example that demonstrates good variable naming:

# Good variable naming practices
total_students = 25
average_score = 78.5
is_enrolled = True
course_name = "Introduction to Python"
# Bad variable naming practices
x = 25
y = 78.5
z = True
cn = "Introduction to Python"

Following these naming rules and conventions will make your code more readable, maintainable, and understandable to others.