Source code for wemake_python_styleguide.violations.best_practices

# -*- coding: utf-8 -*-

"""
These checks ensure that you follow the best practices.

The source for these best practices is hidden inside countless hours
we have spent debugging software or reviewing it.

How do we find inspiration for new rules?
We find some ugly code during code reviews and audits.
Then we forbid to use this bad code forever.
So, this error will never return to our codebase.

.. currentmodule:: wemake_python_styleguide.violations.best_practices

Summary
-------

.. autosummary::
   :nosignatures:

   WrongMagicCommentViolation
   WrongDocCommentViolation
   OveruseOfNoqaCommentViolation
   OveruseOfNoCoverCommentViolation
   ComplexDefaultValueViolation
   LoopVariableDefinitionViolation
   ContextManagerVariableDefinitionViolation
   MutableModuleConstantViolation
   SameElementsInConditionViolation
   HeterogenousCompareViolation
   WrongModuleMetadataViolation
   EmptyModuleViolation
   InitModuleHasLogicViolation
   BadMagicModuleFunctionViolation
   WrongUnpackingViolation
   DuplicateExceptionViolation
   YieldInComprehensionViolation
   NonUniqueItemsInHashViolation
   BaseExceptionSubclassViolation
   TryExceptMultipleReturnPathViolation
   WrongKeywordViolation
   WrongFunctionCallViolation
   FutureImportViolation
   RaiseNotImplementedViolation
   BaseExceptionViolation
   BooleanPositionalArgumentViolation
   LambdaInsideLoopViolation
   UnreachableCodeViolation
   StatementHasNoEffectViolation
   MultipleAssignmentsViolation
   NestedFunctionViolation
   NestedClassViolation
   MagicNumberViolation
   NestedImportViolation
   ReassigningVariableToItselfViolation
   ListMultiplyViolation
   ProtectedModuleViolation
   ProtectedAttributeViolation
   StopIterationInsideGeneratorViolation
   WrongUnicodeEscapeViolation
   BlockAndLocalOverlapViolation
   ControlVarUsedAfterBlockViolation
   OuterScopeShadowingViolation
   UnhashableTypeInHashViolation
   WrongKeywordConditionViolation
   WrongNamedKeywordViolation
   ApproximateConstantViolation
   StringConstantRedefinedViolation
   IncorrectExceptOrderViolation
   FloatKeyViolation

Best practices
--------------

.. autoclass:: WrongMagicCommentViolation
.. autoclass:: WrongDocCommentViolation
.. autoclass:: OveruseOfNoqaCommentViolation
.. autoclass:: OveruseOfNoCoverCommentViolation
.. autoclass:: ComplexDefaultValueViolation
.. autoclass:: LoopVariableDefinitionViolation
.. autoclass:: ContextManagerVariableDefinitionViolation
.. autoclass:: MutableModuleConstantViolation
.. autoclass:: SameElementsInConditionViolation
.. autoclass:: HeterogenousCompareViolation
.. autoclass:: WrongModuleMetadataViolation
.. autoclass:: EmptyModuleViolation
.. autoclass:: InitModuleHasLogicViolation
.. autoclass:: BadMagicModuleFunctionViolation
.. autoclass:: WrongUnpackingViolation
.. autoclass:: DuplicateExceptionViolation
.. autoclass:: YieldInComprehensionViolation
.. autoclass:: NonUniqueItemsInHashViolation
.. autoclass:: BaseExceptionSubclassViolation
.. autoclass:: TryExceptMultipleReturnPathViolation
.. autoclass:: WrongKeywordViolation
.. autoclass:: WrongFunctionCallViolation
.. autoclass:: FutureImportViolation
.. autoclass:: RaiseNotImplementedViolation
.. autoclass:: BaseExceptionViolation
.. autoclass:: BooleanPositionalArgumentViolation
.. autoclass:: LambdaInsideLoopViolation
.. autoclass:: UnreachableCodeViolation
.. autoclass:: StatementHasNoEffectViolation
.. autoclass:: MultipleAssignmentsViolation
.. autoclass:: NestedFunctionViolation
.. autoclass:: NestedClassViolation
.. autoclass:: MagicNumberViolation
.. autoclass:: NestedImportViolation
.. autoclass:: ReassigningVariableToItselfViolation
.. autoclass:: ListMultiplyViolation
.. autoclass:: ProtectedModuleViolation
.. autoclass:: ProtectedAttributeViolation
.. autoclass:: StopIterationInsideGeneratorViolation
.. autoclass:: WrongUnicodeEscapeViolation
.. autoclass:: BlockAndLocalOverlapViolation
.. autoclass:: ControlVarUsedAfterBlockViolation
.. autoclass:: OuterScopeShadowingViolation
.. autoclass:: UnhashableTypeInHashViolation
.. autoclass:: WrongKeywordConditionViolation
.. autoclass:: WrongNamedKeywordViolation
.. autoclass:: ApproximateConstantViolation
.. autoclass:: StringConstantRedefinedViolation
.. autoclass:: IncorrectExceptOrderViolation
.. autoclass:: FloatKeyViolation

"""

from typing_extensions import final

from wemake_python_styleguide.violations.base import (
    ASTViolation,
    SimpleViolation,
    TokenizeViolation,
)


[docs]@final class WrongMagicCommentViolation(SimpleViolation): """ Restricts to use several control (or magic) comments. We do not allow to use: 1. ``# noqa`` comment without specified violations 2. ``# type: some_type`` comments to specify a type for ``typed_ast`` This violation is reported at the top of the module, so it cannot be locally ignored. Reasoning: We cover several different use-cases in a single rule. ``# noqa`` comment is restricted because it can hide other violations. ``# type: some_type`` comment is restricted because we can already use type annotations instead. Solution: Use ``# noqa`` comments with specified error types. Use type annotations to specify types. We still allow to use ``# type: ignore`` comment. Since sometimes it is totally required. Example:: # Correct: type = MyClass.get_type() # noqa: A001 coordinate: int = 10 some.int_field = 'text' # type: ignore number: int for number in some_untyped_iterable(): ... # Wrong: type = MyClass.get_type() # noqa coordinate = 10 # type: int .. versionadded:: 0.1.0 """ code = 400 error_template = 'Found wrong magic comment: {0}'
[docs]@final class WrongDocCommentViolation(TokenizeViolation): """ Forbids to use empty doc comments (``#:``). Reasoning: Doc comments are used to provide a documentation. But supplying empty doc comments breaks this use-case. It is unclear why they can be used with no contents. Solution: Add some documentation to this comment. Or remove it. Empty doc comments are not caught by the default ``pycodestyle`` checks. Example:: # Correct: #: List of allowed names: NAMES_WHITELIST = ['feature', 'bug', 'research'] # Wrong: #: NAMES_WHITELIST = ['feature', 'bug', 'research'] .. versionadded:: 0.1.0 """ code = 401 error_template = 'Found wrong doc comment'
[docs]@final class OveruseOfNoqaCommentViolation(SimpleViolation): """ Forbids to use too many ``# noqa`` comments. We count it on a per-module basis. We use :str:`wemake_python_styleguide.constants.MAX_NOQA_COMMENTS` as a hard limit. Reasoning: Having too many ``# noqa`` comments make your code less readable and clearly indicates that there's something wrong with it. Solution: Refactor your code to match our style. Or use a config file to switch off some checks. Configuration: This rule is configurable with ``--max-noqa-comments``. Default: :str:`wemake_python_styleguide.options.defaults.MAX_NOQA_COMMENTS` .. versionadded:: 0.7.0 """ error_template = 'Found `noqa` comments overuse: {0}' code = 402
[docs]@final class OveruseOfNoCoverCommentViolation(SimpleViolation): """ Forbids to use too many ``# pragma: no cover`` comments. We count it on a per-module basis. We use :str:`wemake_python_styleguide.constants.MAX_NO_COVER_COMMENTS` as a default value. Reasoning: Having too many ``# pragma: no cover`` comments clearly indicates that there's something wrong with it. Moreover, it makes your tests useless, since they do not cover a big partion of your code. Solution: Refactor your code to much the style. Or use a config file to switch off some checks. .. versionadded:: 0.8.0 """ error_template = 'Found `noqa` comments overuse: {0}' code = 403
[docs]@final class ComplexDefaultValueViolation(ASTViolation): """ Forbids to use complex defaults. Anything that is not a ``ast.Name``, ``ast.Attribute``, ``ast.Str``, ``ast.NameConstant``, ``ast.Tuple``, ``ast.Bytes``, ``ast.Num`` or ``ast.Ellipsis`` should be moved out from defaults. Reasoning: It can be tricky. Nothing stops you from making database calls or http requests in such expressions. It is also not readable for us. Solution: Move the expression out from default value. Example:: # Correct: SHOULD_USE_DOCTEST = 'PYFLAKES_DOCTEST' in os.environ def __init__(self, with_doctest=SHOULD_USE_DOCTEST): # Wrong: def __init__(self, with_doctest='PYFLAKES_DOCTEST' in os.environ): .. versionadded:: 0.8.0 .. versionchanged:: 0.11.0 """ error_template = 'Found complex default value' code = 404 previous_codes = {459}
[docs]@final class LoopVariableDefinitionViolation(ASTViolation): """ Forbids to use anything rather than ``ast.Name`` to define loop variables. Reasoning: When defining a ``for`` loop with attributes, indexes, calls, or any other nodes it does dirty things inside. Solution: Use regular ``ast.Name`` variables. Or tuple of ``ast.Name`` variables. Star names are also fine. Example:: # Correct: for person in database.people(): ... # Wrong: for context['person'] in database.people(): ... .. versionadded:: 0.8.0 .. versionchanged:: 0.11.0 """ error_template = 'Found wrong `for` loop variable definition' code = 405 previous_codes = {460}
[docs]@final class ContextManagerVariableDefinitionViolation(ASTViolation): """ Forbids to use anything rather than ``ast.Name`` to define contexts. Reasoning: When defining a ``with`` context managers with attributes, indexes, calls, or any other nodes it does dirty things inside. Solution: Use regular ``ast.Name`` variables. Or tuple of ``ast.Name`` variables. Star names are also fine. Example:: # Correct: with open('README.md') as readme: ... # Wrong: with open('README.md') as files['readme']: ... .. versionadded:: 0.8.0 .. versionchanged:: 0.11.0 """ error_template = 'Found wrong context manager variable definition' code = 406 previous_codes = {461}
[docs]@final class MutableModuleConstantViolation(ASTViolation): """ Forbids mutable constants on a module level. Reasoning: Constants should be immutable. Solution: Use immutable types for constants. We only treat ``ast.Set``, ``ast.Dict``, ``ast.List``, and comprehensions as mutable things. All other nodes are still fine. Example:: # Correct: import types CONST1 = frozenset((1, 2, 3)) CONST2 = (1, 2, 3) CONST3 = types.MappingProxyType({'key': 'value'}) # Wrong: CONST1 = {1, 2, 3} CONST2 = [x for x in some()] CONST3 = {'key': 'value'} .. versionadded:: 0.10.0 .. versionchanged:: 0.11.0 """ error_template = 'Found mutable module constant' code = 407 previous_codes = {466}
[docs]@final class SameElementsInConditionViolation(ASTViolation): """ Forbids to use the same logical conditions in one expression. Reasoning: Using the same name in logical condition more that once indicates that you are either making a logical mistake, or just over-complicating your design. Solution: Remove the duplicating condition. Example:: # Correct: if some_value or other_value: ... # Wrong: if some_value or some_value: ... .. versionadded:: 0.10.0 .. versionchanged:: 0.11.0 .. versionchanged:: 0.13.0 """ error_template = 'Found duplicate logical condition' code = 408 previous_codes = {469}
[docs]@final class HeterogenousCompareViolation(ASTViolation): """ Forbids to heterogenous operators in one compare. Note, that we allow to mix ``>`` with ``>=`` and ``<`` with ``<=`` operators. Reasoning: This is hard to read and understand. Solution: Refactor the expression to have separate parts joined with ``and`` boolean operator. Example:: # Correct: if x == y == z: ... if x > y >= z: ... # Wrong: if x > y == 5: ... if x == y != z: ... .. versionadded:: 0.10.0 .. versionchanged:: 0.11.0 """ error_template = 'Found heterogenous compare' code = 409 previous_codes = {471}
[docs]@final class WrongModuleMetadataViolation(ASTViolation): """ Forbids to have some module level variables. Reasoning: We discourage using module variables like ``__author__``, because code should not contain any metadata. Solution: Place all the metadata in ``setup.py``, ``setup.cfg``, or ``pyproject.toml``. Use proper docstrings and packaging classifiers. Use ``pkg_resources`` if you need to import this data into your app. See :py:data:`~wemake_python_styleguide.constants.MODULE_METADATA_VARIABLES_BLACKLIST` for full list of bad names. Example:: # Wrong: __author__ = 'Nikita Sobolev' __version__ = 0.1.2 .. versionadded:: 0.1.0 """ error_template = 'Found wrong metadata variable: {0}' code = 410
[docs]@final class EmptyModuleViolation(SimpleViolation): """ Forbids to have empty modules. Reasoning: Why is it even there? Do not pollute your project with empty files. Solution: If you have an empty module there are two ways to handle that: 1. delete it 2. drop some documentation in it, so you will explain why it is there .. versionadded:: 0.1.0 """ error_template = 'Found empty module' code = 411
[docs]@final class InitModuleHasLogicViolation(SimpleViolation): """ Forbids to have logic inside ``__init__`` module. Reasoning: If you have logic inside the ``__init__`` module it means several things: 1. you are keeping some outdated stuff there, you need to refactor 2. you are placing this logic into the wrong file, just create another one 3. you are doing some dark magic, and you should not do that Solution: Put your code in other modules. However, we allow to have some contents inside the ``__init__`` module: 1. comments, since they are dropped before AST comes in play 2. docs string, because sometimes it is required to state something It is also fine when you have different users that use your code. And you do not want to break everything for them. In this case this rule can be configured. 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 """ error_template = 'Found `__init__.py` module with logic' code = 412
[docs]@final class BadMagicModuleFunctionViolation(ASTViolation): """ Forbids to use ``__getattr__`` and ``__dir__`` module magic methods. Reasoning: It does not bring any features, only making it harder to understand what is going on. Solution: Refactor your code to use custom methods instead. 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:: 0.9.0 """ error_template = 'Found bad magic module function: {0}' code = 413
[docs]@final class WrongUnpackingViolation(ASTViolation): """ Forbids to have tuple unpacking with side-effects. Reasoning: Having unpacking with side-effects is very dirty. You might get in serious and very hard-to-debug troubles because of this technique. So, do not use it. Solution: Use unpacking with only variables, not any other entities. Example:: # Correct: first, second = some() # Wrong: first, some_dict['alias'] = some() .. versionadded:: 0.6.0 .. versionchanged:: 0.11.0 """ error_template = 'Found incorrect unpacking target' code = 414 previous_codes = {446}
[docs]@final class DuplicateExceptionViolation(ASTViolation): """ Forbids to have the same exception class in multiple ``except`` blocks. Reasoning: Having the same exception name in different blocks means that something is not right: since only one branch will work. Other one will always be ignored. So, that is clearly an error. Solution: Use unique exception handling rules. Example:: # Correct: try: ... except ValueError: ... # Wrong: try: ... except ValueError: ... except ValueError: ... .. versionadded:: 0.6.0 .. versionchanged:: 0.11.0 """ error_template = 'Found duplicate exception: {0}' code = 415 previous_codes = {447}
[docs]@final class YieldInComprehensionViolation(ASTViolation): """ Forbids to have ``yield`` keyword inside comprehensions. Reasoning: Having the ``yield`` keyword inside comprehensions is error-prone. You can shoot yourself in a foot by an inaccurate usage of this feature. Solution: Use regular ``for`` loops with ``yield`` keywords. Or create a separate generator function. Example:: # Wrong: list((yield letter) for letter in 'ab') # Will resilt in: ['a', None, 'b', None] list([(yield letter) for letter in 'ab']) # Will result in: ['a', 'b'] See also: https://github.com/satwikkansal/wtfPython#-yielding-none .. versionadded:: 0.7.0 .. versionchanged:: 0.11.0 """ error_template = 'Found `yield` inside comprehension' code = 416 previous_codes = {448}
[docs]@final class NonUniqueItemsInHashViolation(ASTViolation): """ Forbids to have duplicate items in hashes. Reasoning: When you explicitly put duplicate items in ``set`` literals or in ``dict`` keys it just does not make any sense. Since hashes cannot contain duplicate items and they will be removed anyway. Solution: Remove duplicate items. Example:: # Correct: some_set = {'a', variable1} some_set = {make_call(), make_call()} # Wrong: some_set = {'a', 'a', variable1, variable1} Things that we consider duplicates: builtins and variables. These nodes are not checked because they may return different results: - function and method calls - comprehensions - attributes - subscribe operations .. versionadded:: 0.7.0 .. versionchanged:: 0.11.0 .. versionchanged:: 0.12.0 """ error_template = 'Found non-unique item in hash: {0}' code = 417 previous_codes = {449}
[docs]@final class BaseExceptionSubclassViolation(ASTViolation): """ Forbids to have duplicate items in ``set`` literals. Reasoning: ``BaseException`` is a special case: it is not designed to be extended by users. A lot of your ``except Exception`` cases won't work. That's incorrect and dangerous. Solution: Change the base class to ``Exception``. Example:: # Correct: class MyException(Exception): ... # Wrong: class MyException(BaseException): ... See also: https://docs.python.org/3/library/exceptions.html#exception-hierarchy .. versionadded:: 0.7.0 .. versionchanged:: 0.11.0 """ error_template = 'Found exception inherited from `BaseException`' code = 418 previous_codes = {450}
[docs]@final class TryExceptMultipleReturnPathViolation(ASTViolation): """ Forbids to use multiple returning paths with ``try`` / ``except`` case. Note, that we check for any ``return``, ``break``, or ``raise`` nodes. Reasoning: The problem with ``return`` in ``else`` and ``finally`` is that it is impossible to say what value is going to be actually returned without looking up the implementation details. Why? Because ``return`` does not expect that some other code will be executed after it. But, ``finally`` is always executed, even after ``return``. And ``else`` will not be executed when there are no exceptions in ``try`` case and a ``return`` statement. Solution: Remove ``return`` from one of the cases. Example:: # Correct: try: return 1 except YourException: ... finally: clear_things_up() # Wrong: try: return 1 # this line will never return except Exception: ... finally: return 2 # this line will actually return try: return 1 # this line will actually return except ZeroDivisionError: ... else: return 0 # this line will never return .. versionadded:: 0.7.0 .. versionchanged:: 0.11.0 .. versionchanged:: 0.12.0 """ error_template = 'Found `try`/`else`/`finally` with multiple return paths' code = 419 previous_codes = {458}
[docs]@final class WrongKeywordViolation(ASTViolation): """ Forbids to use some ``python`` keywords. Reasoning: Using some keywords generally gives you more pain that relieve. ``del`` keyword is not composable with other functions, you cannot pass it as a regular function. It is also quite error-prone due to ``__del__`` magic method complexity and that ``del`` is actually used to nullify variables and delete them from the execution scope. Moreover, it has a lot of substitutions. You won't miss it! ``pass`` keyword is just useless by design. There's no usecase for it. Because it does literally nothing. ``global`` and ``nonlocal`` promote bad-practices of having an external mutable state somewhere. This solution does not scale. And leads to multiple possible mistakes in the future. Solution: Solutions differ from keyword to keyword. ``pass`` should be replaced with docstring or ``contextlib.suppress``. ``del`` should be replaced with specialized methods like ``.pop()``. ``global`` and ``nonlocal`` usages should be refactored. .. versionadded:: 0.1.0 """ error_template = 'Found wrong keyword: {0}' code = 420
[docs]@final class WrongFunctionCallViolation(ASTViolation): """ Forbids to call some built-in functions. Reasoning: Some functions are only suitable for very specific use cases, we forbid to use them in a free manner. See :py:data:`~wemake_python_styleguide.constants.FUNCTIONS_BLACKLIST` for the full list of blacklisted functions. See also: https://www.youtube.com/watch?v=YjHsOrOOSuI .. versionadded:: 0.1.0 """ error_template = 'Found wrong function call: {0}' code = 421
[docs]@final class FutureImportViolation(ASTViolation): """ Forbids to use ``__future__`` imports. Reasoning: Almost all ``__future__`` imports are legacy ``python2`` compatibility tools that are no longer required. Solution: Remove them. Drop ``python2`` support. Except, there are some new ones for ``python4`` support. See :py:data:`~wemake_python_styleguide.constants.FUTURE_IMPORTS_WHITELIST` for the full list of allowed future imports. Example:: # Correct: from __future__ import annotations # Wrong: from __future__ import print_function .. versionadded:: 0.1.0 """ error_template = 'Found future import: {0}' code = 422
[docs]@final class RaiseNotImplementedViolation(ASTViolation): """ Forbids to use ``NotImplemented`` error. Reasoning: These two violations look so similar. But, these violations have different use cases. Use cases of ``NotImplemented`` is too limited to be generally available. Solution: Use ``NotImplementedError``. Example:: # Correct: raise NotImplementedError('To be done') # Wrong: raise NotImplemented .. versionadded:: 0.1.0 See also: https://stackoverflow.com/a/44575926/4842742 """ error_template = 'Found raise NotImplemented' code = 423
[docs]@final class BaseExceptionViolation(ASTViolation): """ Forbids to use ``BaseException`` exception. Reasoning: We can silence system exit and keyboard interrupt with this exception handler. It is almost the same as raw ``except:`` block. Solution: Handle ``Exception``, ``KeyboardInterrupt``, ``GeneratorExit``, and ``SystemExit`` separately. Do not use the plain ``except:`` keyword. Example:: # Correct: except Exception as ex: ... # Wrong: except BaseException as ex: ... .. versionadded:: 0.3.0 See also: https://docs.python.org/3/library/exceptions.html#exception-hierarchy https://help.semmle.com/wiki/pages/viewpage.action?pageId=1608527 """ error_template = 'Found except `BaseException`' code = 424
[docs]@final class BooleanPositionalArgumentViolation(ASTViolation): """ Forbids to pass booleans as non-keyword parameters. Reasoning: Passing boolean as regular positional parameters is very non-descriptive. It is almost impossible to tell, what does this parameter means. And you almost always have to look up the implementation to tell what is going on. Solution: Pass booleans as keywords only. This will help you to save extra context on what's going on. Example:: # Correct: UsersRepository.update(cache=True) # Wrong: UsersRepository.update(True) .. versionadded:: 0.6.0 """ error_template = 'Found boolean non-keyword argument: {0}' code = 425
[docs]@final class LambdaInsideLoopViolation(ASTViolation): """ Forbids to use ``lambda`` inside loops. Reasoning: It is error-prone to use ``lambda`` inside ``for`` and ``while`` loops due to the famous late-binding. Solution: Use regular functions, factory functions, or ``partial`` functions. Save yourself from possible confusion. Example:: # Correct: for index in range(10): some.append(partial_function(index)) # Wrong: for index in range(10): some.append(lambda index=index: index * 10)) other.append(lambda: index * 10)) .. versionadded:: 0.5.0 .. versionchanged:: 0.11.0 See also: https://docs.python-guide.org/writing/gotchas/#late-binding-closures """ error_template = "Found `lambda` in loop's body" code = 426 previous_codes = {442}
[docs]@final class UnreachableCodeViolation(ASTViolation): """ Forbids to have unreachable code. What is unreachable code? It is some lines of code that cannot be executed by python's interpreter. This is probably caused by ``return`` or ``raise`` statements. However, we can not cover 100% of truly unreachable code by this rule. This happens due to the dynamic nature of python. For example, detecting that ``1 / some_value`` would sometimes raise an exception is too complicated and is out of the scope of this rule. Reasoning: Having dead code in your project is an indicator that you do not care about your code base at all. It dramatically reduces code quality and readability. It also demotivates team members. Solution: Delete any unreachable code you have. Or refactor it, if this happens by your mistake. Example:: # Correct: def some_function(): print('This line is reachable, all good') return 5 # Wrong: def some_function(): return 5 print('This line is unreachable') .. versionadded:: 0.5.0 .. versionchanged:: 0.11.0 """ error_template = 'Found unreachable code' code = 427 previous_codes = {443}
[docs]@final class StatementHasNoEffectViolation(ASTViolation): """ Forbids to have statements that do nothing. Reasoning: Statements that just access the value or expressions used as statements indicate that your code contains deadlines. They just pollute your codebase and do nothing. Solution: Refactor your code in case it was a typo or error. Or just delete this code. Example:: # Correct: def some_function(): price = 8 + 2 return price # Wrong: def some_function(): 8 + 2 print .. versionadded:: 0.5.0 .. versionchanged:: 0.11.0 """ error_template = 'Found statement that has no effect' code = 428 previous_codes = {444}
[docs]@final class MultipleAssignmentsViolation(ASTViolation): """ Forbids to have multiple assignments on the same line. Reasoning: Multiple assignments on the same line might not do what you think they do. They can also grown pretty long. And you will not notice the rising complexity of your code. Solution: Use separate lines for each assignment. Example:: # Correct: a = 1 b = 1 # Wrong: a = b = 1 .. versionadded:: 0.6.0 .. versionchanged:: 0.11.0 """ error_template = 'Found multiple assign targets' code = 429 previous_codes = {445}
[docs]@final class NestedFunctionViolation(ASTViolation): """ Forbids to have nested functions. Reasoning: Nesting functions is a bad practice. It is hard to test them, it is hard then to separate them. People tend to overuse closures, so it's hard to manage the dataflow. Solution: Just write flat functions, there's no need to nest them. Pass parameters as normal arguments, do not use closures. Until you need them for decorators or factories. We also disallow to nest ``lambda`` and ``async`` functions. See :py:data:`~wemake_python_styleguide.constants.NESTED_FUNCTIONS_WHITELIST` for the whole list of whitelisted names. Example:: # Correct: def do_some(): ... def other(): ... # Wrong: def do_some(): def inner(): ... .. versionadded:: 0.1.0 """ error_template = 'Found nested function: {0}' code = 430
[docs]@final class NestedClassViolation(ASTViolation): """ Forbids to use nested classes. Reasoning: Nested classes are really hard to manage. You can not even create an instance of this class in many cases. Testing them is also really hard. Solution: Just write flat classes, there's no need nest them. If you are nesting classes inside a function for parametrization, then you will probably need to use different design (or metaclasses). Configuration: This rule is configurable with ``--nested-classes-whitelist``. Default: :str:`wemake_python_styleguide.options.defaults.NESTED_CLASSES_WHITELIST` Example:: # Correct: class Some(object): ... class Other(object): ... # Wrong: class Some(object): class Inner(object): ... .. versionadded:: 0.1.0 .. versionchanged:: 0.13.0 """ error_template = 'Found nested class: {0}' code = 431
[docs]@final class MagicNumberViolation(ASTViolation): """ Forbids to use magic numbers in your code. What we call a "magic number"? Well, it is actually any number that appears in your code out of nowhere. Like ``42``. Or ``0.32``. Reasoning: It is very hard to remember what these numbers actually mean. Why were they used? Should they ever be changed? Or are they eternal like ``3.14``? Solution: Give these numbers a name! Move them to a separate variable, giving more context to the reader. And by moving things into new variables you will trigger other complexity checks. Example:: # Correct: price_in_euro = 3.33 # could be changed later total = get_items_from_cart() * price_in_euro # Wrong: total = get_items_from_cart() * 3.33 What are numbers that we exclude from this check? Any numbers that are assigned to a variable, array, dictionary, or keyword arguments inside a function. ``int`` numbers that are in range ``[-10, 10]`` and some other common numbers, that are defined in :py:data:`~wemake_python_styleguide.constants.MAGIC_NUMBERS_WHITELIST` .. versionadded:: 0.1.0 See also: https://en.wikipedia.org/wiki/Magic_number_(programming) """ code = 432 error_template = 'Found magic number: {0}'
[docs]@final class NestedImportViolation(ASTViolation): """ Forbids to have nested imports in functions. Reasoning: Usually, nested imports are used to fix the import cycle. So, nested imports show that there's an issue with your design. Solution: You don't need nested imports, you need to refactor your code. Introduce a new module or find another way to do what you want to do. Rethink how your layered architecture should look like. Example:: # Correct: from my_module import some_function def some(): ... # Wrong: def some(): from my_module import some_function .. versionadded:: 0.1.0 .. versionchanged:: 0.11.0 See also: https://github.com/seddonym/layer_linter """ error_template = 'Found nested import' code = 433 previous_codes = {435}
[docs]@final class ReassigningVariableToItselfViolation(ASTViolation): """ Forbids to assign variable to itself. Reasoning: There is no need to do that. Generally, it is an indication of some errors or just dead code. Example:: # Correct: some = some + 1 x_coord, y_coord = y_coord, x_coord # Wrong: some = some x_coord, y_coord = x_coord, y_coord .. versionadded:: 0.3.0 .. versionchanged:: 0.11.0 """ error_template = 'Found reassigning variable to itself: {0}' code = 434 previous_codes = {438}
[docs]@final class ListMultiplyViolation(ASTViolation): """ Forbids to multiply lists. Reasoning: When you multiply lists - it does not create new values, it creates references to the existing value. It is not what people mean in 99.9% of cases. Solution: Use list comprehension or loop instead. Example:: # Wrong: my_list = [1, 2, 3] * 3 See also: https://github.com/satwikkansal/wtfPython#-explanation-8 .. versionadded:: 0.12.0 """ error_template = 'Found list multiply' code = 435
[docs]@final class ProtectedModuleViolation(ASTViolation): """ Forbids to import protected modules. Reasoning: When importing protected modules we break a contract that authors of this module enforce. This way we are not respecting encapsulation and it may break our code at any moment. Solution: Do not import anything from protected modules. Respect the encapsulation. Example:: # Correct: from some.public.module import FooClass # Wrong: import _compat from some._protected.module import BarClass from some.module import _protected .. versionadded:: 0.3.0 .. versionchanged:: 0.11.0 """ error_template = 'Found protected module import' code = 436 previous_codes = {440}
[docs]@final class ProtectedAttributeViolation(ASTViolation): """ Forbids to use protected attributes and methods. Reasoning: When using protected attributes and method we break a contract that authors of this class enforce. This way we are not respecting encapsulation and it may break our code at any moment. Solution: Do not use protected attributes and methods. Respect the encapsulation. Example:: # Correct: self._protected = 1 cls._hidden_method() some.public() super()._protected() # Wrong: print(some._protected) instance._hidden() self.container._internal = 10 Note, that it is possible to use protected attributes with ``self``, ``cls``, and ``super()`` as base names. We allow this so you can create and use protected attributes and methods inside the class context. This is how protected attributes should be used. .. versionadded:: 0.3.0 .. versionchanged:: 0.11.0 """ error_template = 'Found protected attribute usage: {0}' code = 437 previous_codes = {441}
[docs]@final class StopIterationInsideGeneratorViolation(ASTViolation): """ Forbids to raise ``StopIteration`` inside generators. Reasoning: ``StopIteration`` should not be raised explicitly in generators. Solution: Use return statement to get out of a generator. Example:: # Correct: def some_generator(): if some_value: return yield 1 # Wrong: def some_generator(): if some_value: raise StopIteration yield 1 See also: https://docs.python.org/3/library/exceptions.html#StopIteration .. versionadded:: 0.12.0 """ error_template = 'Found `StopIteration` raising inside generator' code = 438
[docs]@final class WrongUnicodeEscapeViolation(TokenizeViolation): r""" Forbids to use unicode escape sequences in binary strings. Reasoning: Binary strings do not work with unicode. Having unicode escape characters in there means that you have an error in your code. Solution: Use regular strings when escaping unicode strings. Example:: # Correct: escaped = '\u0041' # equals to 'A' # Wrong: escaped = b'\u0040' # equals to b'\\u0040' .. versionadded:: 0.12.0 """ error_template = 'Found unicode escape in a binary string: {0}' code = 439
[docs]@final class BlockAndLocalOverlapViolation(ASTViolation): """ Forbids to local and block variables to overlap. What we call local variables: 1. Assigns and annotations 2. Function arguments (they are local to the function body) What we call block variables: 1. Imports 2. Functions and async functions definitions 3. Classes, methods, and async methods definitions 4. For and async for loops variables 5. Except block exception aliases We allow local variables to overlap theirselfs, we forbid block varibals to overlap theirselfs. Reasoning: A lot of complex errors might happen when you shadow local varibales with block variables or when you shadow block variables with local variables. Solution: Use names that do not overlap. Example:: # Correct: my_value = 1 my_value = my_value + 1 # Wrong: import my_value my_value = 1 # overlaps with import See also: https://github.com/satwikkansal/wtfPython#-explanation-20 .. versionadded:: 0.12.0 """ error_template = 'Found block variables overlap: {0}' code = 440
[docs]@final class ControlVarUsedAfterBlockViolation(ASTViolation): """ Forbids to use control variables after the block body. What we call block control variables: 1. ``for`` loop unpacked variables 2. ``with`` context variables 3. ``except`` exception names Reasoning: Variables leaking from the blocks can damage your logic. It might not contain what you think they contain. Some variables even might be deleted right after the block, just like in ``except Exception as exc:`` where ``exc`` won't be in scope after ``except`` body. Solution: Use names inside the scope they are defined. Create new functions to return values in case you need to use block variables: when searching for a value, etc. Example:: # Correct: for my_item in collection: print(my_item) # Wrong: for my_item in collection: ... print(my_item) See also: https://github.com/satwikkansal/wtfPython#-explanation-32 .. versionadded:: 0.12.0 """ error_template = 'Found control variable used after block: {0}' code = 441
[docs]@final class OuterScopeShadowingViolation(ASTViolation): """ Forbids to shadow variables from outer scopes. We check function, method, and module scopes. While we do not check class scope. Because class level constants are not available via regular name, and they are scope to ``ClassName.var_name``. Reasoning: Shadowing can lead you to a big pile of strage and unexpected bugs. Solution: Use different names and do not allow scoping. Example:: # Correct: def test(): ... def other(): test1 = 1 # Wrong: def test(): ... def other(): test = 1 # shadows `test()` function .. versionadded:: 0.12.0 """ error_template = 'Found outer scope names shadowing: {0}' code = 442
[docs]@final class UnhashableTypeInHashViolation(ASTViolation): """ Forbids to use exlicit unhashable types as set items and dict keys. Reasoning: This will resolve in ``TypeError`` in runtime. Solution: Use hashable types to define set items and dict keys. Example:: # Correct: my_dict = {1: {}, (1, 2): [], (2, 3): {1, 2}} # Wrong: my_dict = {[1, 2]: [], {2, 3}: {1, 2}} .. versionadded:: 0.12.0 """ error_template = 'Found unhashable item' code = 443
[docs]@final class WrongKeywordConditionViolation(ASTViolation): """ Forbids to use exlicit falsly-evaluated conditions with several keywords. We check: - ``ast.While`` - ``ast.Assert`` We do not check variables, attributes, calls, bool and bin operators, etc. We disallow constants and some expressions. Reasoning: Some conditions clearly tell us that this node won't work correctly. So, we need to check that we can fix that. Solution: Remove the unreachable node, or change the condition item. Example:: # Correct: assert some_variable while True: ... # Wrong: assert [] while False: ... .. versionadded:: 0.12.0 .. versionchanged:: 0.13.0 """ error_template = 'Found wrong keyword condition' code = 444
[docs]@final class WrongNamedKeywordViolation(ASTViolation): """ Forbids to have wrong named keywords in starred dicts. Reasoning: Using wrong keywords in starred dict. Eg.: ``print(**{'@': 1})``. Solution: Don't use incorrect identifiers for keywords. Example:: # Correct: print(**{'end': '|'}) # Wrong: print(**{'3end': '|'}) .. versionadded:: 0.13.0 """ code = 445 error_template = 'Found wrong named keyword in starred dict'
[docs]@final class ApproximateConstantViolation(ASTViolation): """ Forbids to use approximate constants. Reasoning: Some constants are already defined. No need to write them again, use existing values. We just compare numbers as strings and raise this violation when they start with the same chars. Solution: Use pre-defined constants. Example:: # Correct: from math import pi random_number = 3.15 too_short = 3.1 # Wrong: pi = 3.14 See :py:data:`~wemake_python_styleguide.constants.MATH_APPROXIMATE_CONSTANTS` for full list of math constants that we check for. See also: https://docs.python.org/3/library/math.html#constants .. versionadded:: 0.13.0 """ code = 446 error_template = 'Found approximate constant: {0}'
[docs]@final class StringConstantRedefinedViolation(ASTViolation): """ Forbid to use alphabet as a string. Reasoning: Some constants are already defined. No need to write them again, use existing values. We just compare strings and raise this violation when they have exactly the same chars. Solution: Use pre-defined constants. Example:: # Correct: import string UPPERCASE_ALPH = string.ascii_uppercase LOWERCASE_ALPH = string.ascii_lowercase # Wrong: GUESS_MY_NAME = "abcde...WXYZ" UPPERCASE_ALPH = "ABCD...WXYZ" LOWERCASE_ALPH = "abcd...wxyz" .. versionadded:: 0.13.0 """ error_template = 'Found alphabet as strings: {0}' code = 447
[docs]@final class IncorrectExceptOrderViolation(ASTViolation): """ Forbids the use of incorrect order of ``except``. Note, we only check for built-in exceptions. Because we cannot statically identify the inheritance order of custom ones. Reasoning: Using incorrect order of exceptions is error-prone, since you end up with some unreachable exception clauses. Solution: Use correct order of exceptions. Example:: # Correct: try: ... except ValueError: ... except Exception: ... # Wrong: try: ... except Exception: ... except ValueError: ... See also: https://bit.ly/36MHlzw .. versionadded:: 0.13.0 """ error_template = 'Found incorrect exception order' code = 448
[docs]@final class FloatKeyViolation(ASTViolation): """ Forbids to define and use ``float`` keys. Reasoning: ``float`` is a very ugly data type. It has a lot of "precision" errors. When we use ``float`` as keys we can hit this wall. We also cannot use ``float`` keys with lists by design. Solution: Use other data types: integers, decimals, or use fuzzy logic. Example:: # Correct: some = {1: 'a'} some[1] # Wrong: some = {1.0: 'a'} some[1.0] .. versionadded:: 0.13.0 """ error_template = 'Found float used as a key' code = 449