Python Naming Conventions

General

• Avoid using names that are too general or too wordy. Strike a good balance between the two.
• Bad: data_structure, my_list, info_map, dictionary_for_the_purpose_of_storing_data_representing_word_definitions
• Good: user_profile, menu_options, word_definitions
• Don’t be a jackass and name things “O”, “l”, or “I”
• When using CamelCase names, capitalize all letters of an abbreviation (e.g. HTTPServer, not HttpServer)

Packages

• Package names should be all lower case
• When multiple words are needed, an underscore should separate them
• It is usually preferable to stick to 1 word names

Modules

• Module names should be all lower case
• When multiple words are needed, an underscore should separate them
• It is usually preferable to stick to 1 word names

Classes

• Class names should follow the UpperCaseCamelCase convention
• Python’s built-in classes, however are typically lowercase words
• Exception classes should end in “Error”

Global (module-level) Variables

• Global variables should be all lowercase
• Words in a global variable name should be separated by an underscore

Instance Variables

• Instance variable names should be all lower case
• Words in an instance variable name should be separated by an underscore
• Non-public instance variables should begin with a single underscore
• If an instance name needs to be mangled, two underscores may begin its name

Methods

• Method names should be all lower case
• Words in an method name should be separated by an underscore
• Non-public method should begin with a single underscore
• If a method name needs to be mangled, two underscores may begin its name

Method Arguments

• Instance methods should have their first argument named ‘self’.
• Class methods should have their first argument named ‘cls’

Functions

• Function names should be all lower case
• Words in a function name should be separated by an underscore

Constants

• Constant names must be fully capitalized
• Words in a constant name should be separated by an underscore

Meaning of underscores

Single or double underscores at the beginning and/or at the end of names have special meanings in Python:

• _single_leading_underscore: Weak “internal use” indicator. For example, from M import * does not import objects whose name starts with an underscore.

• single_trailing_underscore_: Used by convention to avoid conflicts with Python keyword, e.g. class_ instead of class.

• __double_leading_underscore: When naming a class attribute, invokes name mangling (inside class FooBar, __boo becomes _FooBar__boo)

• __double_leading_and_trailing_underscore__: “Magic” objects or attributes that live in user-controlled namespaces. E.g. __init__, __import__ or __file__. Never invent such names; only use them as documented.