Source code for wemake_python_styleguide.violations.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!


- 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 must use ``snake_case``
- One word for a package is the most preferable name


- Modules must use ``snake_case``
- Module names must not overuse magic names
- Module names must be valid Python identifiers


- 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 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``

.. currentmodule:: wemake_python_styleguide.violations.naming


.. autosummary::


Module names

.. autoclass:: WrongModuleNameViolation
.. autoclass:: WrongModuleMagicNameViolation
.. autoclass:: WrongModuleNamePatternViolation

General names

.. autoclass:: WrongVariableNameViolation
.. autoclass:: TooShortNameViolation
.. autoclass:: PrivateNameViolation
.. autoclass:: SameAliasImportViolation
.. autoclass:: UnderscoredNumberNameViolation
.. autoclass:: UpperCaseAttributeViolation
.. autoclass:: ConsecutiveUnderscoresInNameViolation
.. autoclass:: ReservedArgumentNameViolation
.. autoclass:: TooLongNameViolation
.. autoclass:: UnicodeNameViolation
.. autoclass:: TrailingUnderscoreViolation
.. autoclass:: UnusedVariableIsUsedViolation
.. autoclass:: UnusedVariableIsDefinedViolation
.. autoclass:: WrongUnusedVariableNameViolation
.. autoclass:: UnreadableNameViolation
.. autoclass:: BuiltinShadowingViolation


from typing_extensions import final

from wemake_python_styleguide.violations.base import (

[docs]@final class WrongModuleNameViolation(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 ```` module. Solution: Rename your module, reorganize the contents. See :py:data:`~wemake_python_styleguide.constants.MODULE_NAMES_BLACKLIST` for the full list of bad module names. Example:: # Correct: # Wrong: See also: .. versionadded:: 0.1.0 """ error_template = 'Found wrong module name' code = 100
[docs]@final class WrongModuleMagicNameViolation(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 :py:data:`~wemake_python_styleguide.constants.MAGIC_MODULE_NAMES_WHITELIST` for the full list of allowed magic module names. Example:: # Correct: # Wrong: .. versionadded:: 0.1.0 """ error_template = 'Found wrong module magic name' code = 101
[docs]@final class WrongModuleNamePatternViolation(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 :py:data:`~wemake_python_styleguide.constants.MODULE_NAME_PATTERN` to validate the module names. Example:: # Correct: # Wrong: .. versionadded:: 0.1.0 """ error_template = 'Found incorrect module name pattern' code = 102
# General names:
[docs]@final class WrongVariableNameViolation(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 :py:data:`~wemake_python_styleguide.constants.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: :str:`wemake_python_styleguide.options.defaults.ALLOWED_DOMAIN_NAMES` And with ``--forbidden-domain-names``. Default: :str:`wemake_python_styleguide.options.defaults.FORBIDDEN_DOMAIN_NAMES` The options listed above are used to create new variable names' blacklist starting from :py:data:`~wemake_python_styleguide.constants.VARIABLE_NAMES_BLACKLIST`. .. versionadded:: 0.1.0 """ error_template = 'Found wrong variable name: {0}' code = 110
[docs]@final class TooShortNameViolation(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: :str:`wemake_python_styleguide.options.defaults.MIN_NAME_LENGTH` .. versionadded:: 0.1.0 .. versionchanged:: 0.4.0 .. versionchanged:: 0.12.0 """ error_template = 'Found too short name: {0}' code = 111 postfix_template = ViolationPostfixes.less_than
[docs]@final class PrivateNameViolation(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): ... .. versionadded:: 0.1.0 .. versionchanged:: 0.4.0 .. versionchanged:: 0.14.0 """ error_template = 'Found private name pattern: {0}' code = 112
[docs]@final class SameAliasImportViolation(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: :str:`wemake_python_styleguide.options.defaults.I_CONTROL_CODE` .. versionadded:: 0.1.0 .. versionchanged:: 0.13.0 .. versionchanged:: 0.14.0 """ error_template = 'Found same alias import: {0}' code = 113
[docs]@final class UnderscoredNumberNameViolation(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' .. versionadded:: 0.3.0 .. versionchanged:: 0.4.0 """ error_template = 'Found underscored number name pattern: {0}' code = 114
[docs]@final class UpperCaseAttributeViolation(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 .. versionadded:: 0.3.0 """ error_template = 'Found upper-case constant in a class: {0}' code = 115
[docs]@final class ConsecutiveUnderscoresInNameViolation(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. .. versionadded:: 0.3.0 .. versionchanged:: 0.4.0 """ error_template = 'Found consecutive underscores name: {0}' code = 116
[docs]@final class ReservedArgumentNameViolation(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. .. versionadded:: 0.5.0 """ error_template = 'Found name reserved for first argument: {0}' code = 117
[docs]@final class TooLongNameViolation(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: :str:`wemake_python_styleguide.options.defaults.MAX_NAME_LENGTH` .. versionadded:: 0.5.0 """ error_template = 'Found too long name: {0}' code = 118
[docs]@final class UnicodeNameViolation(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 = '' .. versionadded:: 0.5.0 """ error_template = 'Found unicode name: {0}' code = 119
[docs]@final class TrailingUnderscoreViolation(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 .. versionadded:: 0.7.0 """ error_template = 'Found regular name with trailing underscore: {0}' code = 120
[docs]@final class UnusedVariableIsUsedViolation(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. .. versionadded:: 0.7.0 .. versionchanged:: 0.12.0 .. versionchanged:: 0.14.0 """ error_template = 'Found usage of a variable marked as unused: {0}' code = 121
[docs]@final class UnusedVariableIsDefinedViolation(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. .. versionadded:: 0.12.0 """ error_template = 'Found all unused variables definition: {0}' code = 122
[docs]@final class WrongUnusedVariableNameViolation(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() .. versionadded:: 0.12.0 """ error_template = 'Found wrong unused variable name: {0}' code = 123
[docs]@final class UnreadableNameViolation(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 :py:data:`~wemake_python_styleguide.constants.UNREADABLE_CHARACTER_COMBINATIONS` for full list of unreadable combinations. Example:: # Correct: ControlStatement AveragePrice # Wrong: Memo0Output .. versionadded:: 0.14 """ error_template = 'Found unreadable characters combination: {0}' code = 124
[docs]@final class BuiltinShadowingViolation(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. .. versionadded:: 0.14 """ error_template = 'Found builtin shadowing: {0}' code = 125