Naming

Naming is hard! It is, in fact, one of the two hardest problems.

These checks are required to make your application easier to read and understand by multiple people over the long period of time.

Naming convention

Our naming convention tries to cover all possible cases. It is partially automated with this linter, but:

  • Some rules are still WIP

  • Some rules will never be automated, code reviews to the rescue!

General

  • Use only ASCII characters for names

  • Do not use transliteration from any other languages, translate names instead

  • Use clear names, do not use words that do not mean anything like obj

  • Use names of an appropriate length: not too short, not too long

  • Do not mask builtins

  • Do not use unreadable charachter sequences like O0 and Il

  • Protected members should use underscore as the first char

  • Private names with two leading underscores are not allowed

  • If you need to explicitly state that the variable is unused, prefix it with _ or just use _ as a name

  • Do not use variables that are stated to be unused, rename them when actually using them

  • Do not define unused variables unless you are unpacking other values as well

  • Do not use multiple underscores (__) to create unused variables

  • Whenever you want to name your variable similar to a keyword or builtin, use trailing _

  • Do not use consecutive underscores

  • When writing abbreviations in UpperCase capitalize all letters: HTTPAddress

  • When writing abbreviations in snake_case use lowercase: http_address

  • When writing numbers in snake_case do not use extra _ before numbers as in http2_protocol

Packages

  • Packages must use snake_case

  • One word for a package is the most preferable name

Modules

  • Modules must use snake_case

  • Module names must not overuse magic names

  • Module names must be valid Python identifiers

Classes

  • Classes must use UpperCase

  • Python’s built-in classes, however, are typically lowercase words

  • Exception classes must end with Error

Instance attributes

  • Instance attributes must use snake_case with no exceptions

Class attributes

  • Class attributes must use snake_case with no exceptions

  • Enum fields also must use snake_case

Functions and methods

  • Functions and methods must use snake_case with no exceptions

Method and function arguments

  • Instance methods must have their first argument named self

  • Class methods must have their first argument named cls

  • Metaclass methods must have their first argument named mcs

  • Python’s *args and **kwargs should be default names when just passing these values to some other method/function, unless you want to use these values in place, then name them explicitly

Global (module level) variables

  • Global variables must use CONSTANT_CASE

  • Unless other is required by the API, example: urlpatterns in Django

Variables

  • Variables must use snake_case with no exceptions

  • When a variable is unused it must be prefixed with an underscore: _user

Type aliases

  • Must use UpperCase as real classes

  • Must not contain word type in its name

  • Generic types should be called clearly and properly, not just TT or KT or VT

Summary

WrongModuleNameViolation

Forbids to use blacklisted module names.

WrongModuleMagicNameViolation

Forbids to use any magic names except whitelisted ones.

WrongModuleNamePatternViolation

Forbids to use module names that do not match our pattern.

WrongVariableNameViolation

Forbids to have blacklisted variable names.

TooShortNameViolation

Forbids to have too short variable or module names.

PrivateNameViolation

Forbids to have private name pattern.

SameAliasImportViolation

Forbids to use the same alias as the original name in imports.

UnderscoredNumberNameViolation

Forbids to have names with underscored numbers pattern.

UpperCaseAttributeViolation

Forbids to use anything but snake_case for naming class attributes.

ConsecutiveUnderscoresInNameViolation

Forbids to use more than one consecutive underscore in variable names.

ReservedArgumentNameViolation

Forbids to name your variables as self, cls, and mcs.

TooLongNameViolation

Forbids to have long short variable or module names.

UnicodeNameViolation

Forbids to use unicode names.

TrailingUnderscoreViolation

Forbids to use trailing _ for names that do not need it.

UnusedVariableIsUsedViolation

Forbids to have use variables that are marked as unused.

UnusedVariableIsDefinedViolation

Forbids to define explicit unused variables.

WrongUnusedVariableNameViolation

Forbids to define unused variables with multiple underscores.

UnreadableNameViolation

Forbids to have variable or module names which could be difficult to read.

BuiltinShadowingViolation

Forbids to have variable or module names which shadows builtin names.

Module names

class WrongModuleNameViolation(node=None, text=None, baseline=None)[source]

Bases: wemake_python_styleguide.violations.base.SimpleViolation

Forbids to use blacklisted module names.

Reasoning:

Some module names are not expressive enough. It is hard to tell what you can find inside the utils.py module.

Solution:

Rename your module, reorganize the contents.

See MODULE_NAMES_BLACKLIST for the full list of bad module names.

Example:

# Correct:
github.py
views.py

# Wrong:
utils.py
helpers.py

New in version 0.1.0.

error_template = 'Found wrong module name'
code = 100
class WrongModuleMagicNameViolation(node=None, text=None, baseline=None)[source]

Bases: wemake_python_styleguide.violations.base.SimpleViolation

Forbids to use any magic names except whitelisted ones.

Reasoning:

Do not fall in love with magic. There’s no good reason to use magic names when you can use regular names.

See MAGIC_MODULE_NAMES_WHITELIST for the full list of allowed magic module names.

Example:

# Correct:
__init__.py
__main__.py

# Wrong:
__version__.py

New in version 0.1.0.

error_template = 'Found wrong module magic name'
code = 101
class WrongModuleNamePatternViolation(node=None, text=None, baseline=None)[source]

Bases: wemake_python_styleguide.violations.base.SimpleViolation

Forbids to use module names that do not match our pattern.

Reasoning:

Module names must be valid python identifiers. And just like the variable names - module names should be consistent. Ideally, they should follow the same rules. For python world it is common to use snake_case notation.

We use MODULE_NAME_PATTERN to validate the module names.

Example:

# Correct:
__init__.py
some_module_name.py
test12.py

# Wrong:
_some.py
MyModule.py
0001_migration.py

New in version 0.1.0.

error_template = 'Found incorrect module name pattern'
code = 102

General names

class WrongVariableNameViolation(node, text=None, baseline=None)[source]

Bases: wemake_python_styleguide.violations.base.ASTViolation

Forbids to have blacklisted variable names.

Reasoning:

We have found some names that are not expressive enough. However, they appear in the code more than often. All names that we forbid to use could be improved.

Solution:

Try to use a more specific name instead. If you really want to use any of the names from the list, add a prefix or suffix to it. It will serve you well.

See VARIABLE_NAMES_BLACKLIST for the base list of blacklisted variable names.

Example:

# Correct:
html_node_item = None

# Wrong:
item = None
Configuration:

This rule is configurable with --allowed-domain-names. Default: ()

And with --forbidden-domain-names. Default: ()

The options listed above are used to create new variable names’ blacklist starting from VARIABLE_NAMES_BLACKLIST.

New in version 0.1.0.

error_template = 'Found wrong variable name: {0}'
code = 110
class TooShortNameViolation(node=None, text=None, baseline=None)[source]

Bases: wemake_python_styleguide.violations.base.MaybeASTViolation

Forbids to have too short variable or module names.

Reasoning:

It is hard to understand what the variable means and why it is used, if its name is too short.

Solution:

Think of another name. Give more context to it.

This rule checks: modules, variables, attributes, functions, methods, and classes.

We do not count trailing and leading underscores when calculating length.

Example:

# Correct:
x_coordinate = 1
abscissa = 2

# Wrong:
x = 1
y = 2
Configuration:

This rule is configurable with --min-name-length. Default: 2

New in version 0.1.0.

Changed in version 0.4.0.

Changed in version 0.12.0.

error_template = 'Found too short name: {0}'
code = 111
postfix_template = ' < {0}'
class PrivateNameViolation(node=None, text=None, baseline=None)[source]

Bases: wemake_python_styleguide.violations.base.MaybeASTViolation

Forbids to have private name pattern.

Reasoning:

Private is not private in python. So, why should we pretend it is? This might lead to some serious design flaws.

Solution:

Rename your variable or method to be protected. Think about your design, why do you want to make it private? Are there any other ways to achieve what you want?

This rule checks: modules, variables, attributes, functions, and methods.

Example:

# Correct:
def _collect_coverage(self): ...

# Wrong:
def __collect_coverage(self): ...

New in version 0.1.0.

Changed in version 0.4.0.

Changed in version 0.14.0.

error_template = 'Found private name pattern: {0}'
code = 112
class SameAliasImportViolation(node, text=None, baseline=None)[source]

Bases: wemake_python_styleguide.violations.base.ASTViolation

Forbids to use the same alias as the original name in imports.

Reasoning:

Why would you even do this in the first place?

Example:

# Correct:
from os import path

# Wrong:
from os import path as path

When –i-control-code is set to False you can reexport things with as, because mypy might require it with implicit_reexport = False setting turned on.

Configuration:

This rule is configurable with --i-control-code and --i-dont-control-code. Default: True

New in version 0.1.0.

Changed in version 0.13.0.

Changed in version 0.14.0.

error_template = 'Found same alias import: {0}'
code = 113
class UnderscoredNumberNameViolation(node=None, text=None, baseline=None)[source]

Bases: wemake_python_styleguide.violations.base.MaybeASTViolation

Forbids to have names with underscored numbers pattern.

Reasoning:

This is done for consistency in naming.

Solution:

Do not put an underscore between text and numbers, that is confusing. Rename your variable or modules do not include underscored numbers.

This rule checks: modules, variables, attributes, functions, method, and classes. Please, note that putting an underscore that replaces - in some names between numbers are fine, example: ISO-123-456 would become iso123_456.

Example:

# Correct:
star_wars_episode2 = 'awesome!'
iso123_456 = 'some data'

# Wrong:
star_wars_episode_2 = 'not so awesome'
iso_123_456 = 'some data'

New in version 0.3.0.

Changed in version 0.4.0.

error_template = 'Found underscored number name pattern: {0}'
code = 114
class UpperCaseAttributeViolation(node, text=None, baseline=None)[source]

Bases: wemake_python_styleguide.violations.base.ASTViolation

Forbids to use anything but snake_case for naming class attributes.

Reasoning:

Constants with upper-case names belong on a module level.

Solution:

Move your constants to the module level. Rename your variables so that they conform to snake_case convention.

Example:

# Correct:
MY_MODULE_CONSTANT = 1
class A(object):
    my_attribute = 42

# Wrong:
class A(object):
    MY_CONSTANT = 42

New in version 0.3.0.

error_template = 'Found upper-case constant in a class: {0}'
code = 115
class ConsecutiveUnderscoresInNameViolation(node=None, text=None, baseline=None)[source]

Bases: wemake_python_styleguide.violations.base.MaybeASTViolation

Forbids to use more than one consecutive underscore in variable names.

Reasoning:

This is done to gain extra readability. This naming rule already exists for module names.

Example:

# Correct:
some_value = 5
__magic__ = 5

# Wrong:
some__value = 5

This rule checks: modules, variables, attributes, functions, and methods.

New in version 0.3.0.

Changed in version 0.4.0.

error_template = 'Found consecutive underscores name: {0}'
code = 116
class ReservedArgumentNameViolation(node, text=None, baseline=None)[source]

Bases: wemake_python_styleguide.violations.base.ASTViolation

Forbids to name your variables as self, cls, and mcs.

Reasoning:

These names are special, they should only be used as first arguments inside methods.

Example:

# Correct:
class Test(object):
    def __init__(self):
        ...

# Wrong:
cls = 5
lambda self: self + 12

This rule checks: functions and methods. Having any reserved names in lambda functions is not allowed.

New in version 0.5.0.

error_template = 'Found name reserved for first argument: {0}'
code = 117
class TooLongNameViolation(node=None, text=None, baseline=None)[source]

Bases: wemake_python_styleguide.violations.base.MaybeASTViolation

Forbids to have long short variable or module names.

Reasoning:

Too long names are unreadable. It is better to use a shorter alternative. Long names also indicate that this variable is too complex, maybe it may require some documentation.

Solution:

Think of another name. Give less context to it.

This rule checks: modules, variables, attributes, functions, methods, and classes.

Example:

# Correct:
total_price = 25
average_age = 45

# Wrong:
final_price_after_fifteen_percent_sales_tax_and_gratuity = 30
total_age_of_all_participants_in_the_survey_divided_by_twelve = 2
Configuration:

This rule is configurable with --max-name-length. Default: 45

New in version 0.5.0.

error_template = 'Found too long name: {0}'
code = 118
class UnicodeNameViolation(node=None, text=None, baseline=None)[source]

Bases: wemake_python_styleguide.violations.base.MaybeASTViolation

Forbids to use unicode names.

Reasoning:

This should be forbidden for sanity, readability, and writability.

Solution:

Rename your entities so that they contain only ASCII symbols.

This rule checks: modules, variables, attributes, functions, methods, and classes.

Example:

# Correct:
some_variable = 'Text with russian: русский язык'

# Wrong:
переменная = 42
some_變量 = ''

New in version 0.5.0.

error_template = 'Found unicode name: {0}'
code = 119
class TrailingUnderscoreViolation(node, text=None, baseline=None)[source]

Bases: wemake_python_styleguide.violations.base.ASTViolation

Forbids to use trailing _ for names that do not need it.

Reasoning:

We use trailing underscore for a reason: to indicate that this name shadows a built-in or keyword. So, when overusing this feature for general names: it just harms readability of your program.

Solution:

Rename your variable not to contain trailing underscores.

This rule checks: variables, attributes, functions, methods, and classes.

Example:

# Correct:
class_ = SomeClass
list_ = []

# Wrong:
some_variable_ = 1

New in version 0.7.0.

error_template = 'Found regular name with trailing underscore: {0}'
code = 120
class UnusedVariableIsUsedViolation(node, text=None, baseline=None)[source]

Bases: wemake_python_styleguide.violations.base.ASTViolation

Forbids to have use variables that are marked as unused.

We discourage using variables that start with _ only inside functions and methods as local variables.

However, we allow to use _ because tools like ipython, babel, and django enforce it.

Reasoning:

Sometimes you start to use new logic in your functions, and you start to use variables that once were marked as unused. But, you have not renamed them for some reason. And now you have a lot of confusion: the variable is marked as unused, but you are using it. Why? What’s going on?

Solution:

Rename your variable to be a regular variable without a leading underscore. This way it is declared to be used.

Example:

# Correct:
def function():
    first = 15
    return first + 10

# Wrong:
def function():
    _first = 15
    return _first + 10

This rule checks: functions, methods, and lambda functions.

New in version 0.7.0.

Changed in version 0.12.0.

Changed in version 0.14.0.

error_template = 'Found usage of a variable marked as unused: {0}'
code = 121
class UnusedVariableIsDefinedViolation(node, text=None, baseline=None)[source]

Bases: wemake_python_styleguide.violations.base.ASTViolation

Forbids to define explicit unused variables.

Reasoning:

While it is ok to define unused variables when you have to, like when unpacking a tuple, it is totally not ok to define explicit unusued variables in cases like assignment, function return, exception handling, or context managers. Why do you need this explicitly unused variables?

Solution:

Remove all unused variables definition.

Example:

# Correct:
my_function()
first, _second = some_tuple()
print(first)

# Wrong:
_ = my_function()
_first, _second = some_tuple()

This rule checks: assigns, context managers, except clauses.

New in version 0.12.0.

error_template = 'Found all unused variables definition: {0}'
code = 122
class WrongUnusedVariableNameViolation(node, text=None, baseline=None)[source]

Bases: wemake_python_styleguide.violations.base.ASTViolation

Forbids to define unused variables with multiple underscores.

Reasoning:

We only use _ as a special definition for an unused variable. Other variables are hard to read. It is unclear why would one use it.

Solution:

Rename unused variables to _ or give it some more context with an explicit name: _context.

Example:

# Correct:
some_element, _next_element, _ = some_tuple()
some_element, _, _ = some_tuple()
some_element, _ = some_tuple()

# Wrong:
some_element, _, __  = some_tuple()

New in version 0.12.0.

error_template = 'Found wrong unused variable name: {0}'
code = 123
class UnreadableNameViolation(node=None, text=None, baseline=None)[source]

Bases: wemake_python_styleguide.violations.base.MaybeASTViolation

Forbids to have variable or module names which could be difficult to read.

Reasoning:

Currently one can name your classes like so: ZerO0 Inside it is just O and 0, but we cannot tell it from the word. There are a lot other combinations which are unreadable.

Solution:

Rename your entity not to contain unreadable sequences.

This rule checks: modules, variables, attributes, functions, methods, and classes.

See UNREADABLE_CHARACTER_COMBINATIONS for full list of unreadable combinations.

Example:

# Correct:
ControlStatement
AveragePrice

# Wrong:
Memo0Output

New in version 0.14.

error_template = 'Found unreadable characters combination: {0}'
code = 124
class BuiltinShadowingViolation(node, text=None, baseline=None)[source]

Bases: wemake_python_styleguide.violations.base.ASTViolation

Forbids to have variable or module names which shadows builtin names.

Reasoning:

Your code simply breaks Python. After you create list = 1, you cannot not call builtin function list and what can be worse than that?

Solution:

Rename your entity to not shadow Python builtins.

Example:

# Correct:
my_list = list(some_other)

# Wrong:
str = ''
list = [1, 2, 3]

This can also cause problems when defining class attributes, for example:

class A:
    min = 5
    max = min(10, 20)  # TypeError: 'int' object is not callable

If you feel it is still necesarry to use such a class attribute, consider using a noqa comment with caution.

New in version 0.14.

error_template = 'Found builtin shadowing: {0}'
code = 125