Table of Contents Link to heading

• Rules
• The Python Keywords
• Use of Underscores
• Readability Matters
• Style of Naming Variables
• Sample Variable Names
• Reference
• Further Research

Rules Link to heading

Although you are allowed to make up your own names for variables, you must follow these rules:

1. You cannot use one of Python's keywords as a variable name

2. A variable or function name cannot contain spaces, underscore characters '_'
   can be used instead.

3. The first character must be one of the letters a..z, A..Z, or '_'.

4. After the first character, you may use the letters a..z, A..Z, the digits
   0..0, or '_'.

5. Uppercase and lowercase characters are distinct. This means that the variable
   named 'ItemsOrdered' is not akin to the one named 'itemsordered'.

The Python Keywords Link to heading

Keywords define the language’s syntax rules and structure, and they cannot be used as variable names. Python has thirty-something keywords (and every now and again improvements to Python introduce or eliminate one or two):

Use of Underscores Link to heading

With regards to naming variables, names with leading underscores are intended to have special meaning in Object-Oriented Programming (OOP).

• The use of ‘_’ implies protected attributes (e.g. _init_).
• The use of ‘__’ implies private attributes (e.g. __init__).

Readability Matters Link to heading

Because a variable’s name should reflect the variable’s purpose, programmers often find themselves creating names that are made of multiple words. For example, consider the following variable names:

• coursecode
• studentfullname
• addressline1

Unfortunately, these names are not easily read by the human eye because the words aren’t separated. Because we can’t have spaces in variable names, we need to find another way to separate the words in a multi-word variable name and make it more readable to the human eye.

One way to do this is to use the underscore character to represent a space. For example, the following variable names are easier to read than those previously shown:

• gross_pay
• pay_rate
• hot_dogs_sold_today

Style of Naming Variables Link to heading

The rules above are called snake_case style which is used to name almost every variable in Python (including functions, lists, dictionaries, etc.).

On the other hand, there are other styles in Python used for certain variables namely PascalCase and camelCase.

PascalCase is used to name classes and is written in the following manner:

1. The first character of every word is written in uppercase.
2. There is not a space character.

For example:

• ItemInOrder
• CourseDetail

camelCase is used to name methods (functions belong to a class) and is written in the following manner:

1. The variable name begins with lowercase letters.
2. The first character of the second and subsequent words is written in uppercase.
3. There is not a space character.

For example:

• firstName
• payRate

NOTE: This style of naming is called camelCase because the uppercase characters that appear in a name may suggest a camel’s humps.

Sample Variable Names Link to heading

Reference Link to heading

Gaddis, T 2021, Starting Out With Python, 5th edn, Pearson Education, Inc.

Further Research Link to heading

For a comprehensive, complete documentation, please see PEP-8.