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


.. autosummary::



.. autoclass:: WrongMagicCommentViolation
.. autoclass:: WrongDocCommentViolation
.. autoclass:: OveruseOfNoqaCommentViolation


.. autoclass:: WrongModuleMetadataViolation
.. autoclass:: EmptyModuleViolation
.. autoclass:: InitModuleHasLogicViolation

.. autoclass:: WrongKeywordViolation
.. autoclass:: WrongFunctionCallViolation
.. autoclass:: FutureImportViolation
.. autoclass:: RaiseNotImplementedViolation
.. autoclass:: BaseExceptionViolation
.. autoclass:: BooleanPositionalArgumentViolation


.. autoclass:: NestedFunctionViolation
.. autoclass:: NestedClassViolation
.. autoclass:: MagicNumberViolation
.. autoclass:: StaticMethodViolation
.. autoclass:: BadMagicMethodViolation
.. autoclass:: NestedImportViolation
.. autoclass:: RedundantLoopElseViolation
.. autoclass:: RedundantFinallyViolation
.. autoclass:: ReassigningVariableToItselfViolation
.. autoclass:: YieldInsideInitViolation
.. autoclass:: ProtectedModuleViolation
.. autoclass:: ProtectedAttributeViolation
.. autoclass:: LambdaInsideLoopViolation
.. autoclass:: UnreachableCodeViolation
.. autoclass:: StatementHasNoEffectViolation
.. autoclass:: MultipleAssignmentsViolation
.. autoclass:: IncorrectUnpackingViolation
.. autoclass:: DuplicateExceptionViolation
.. autoclass:: YieldInComprehensionViolation
.. autoclass:: NonUniqueItemsInSetViolation
.. autoclass:: BaseExceptionSubclassViolation
.. autoclass:: SimplifiableIfViolation
.. autoclass:: IncorrectClassBodyContentViolation
.. autoclass:: MethodWithoutArgumentsViolation
.. autoclass:: IncorrectBaseClassViolation
.. autoclass:: IncorrectSlotsViolation
.. autoclass:: IncorrectSuperCallViolation
.. autoclass:: RedundantReturningElseViolation
.. autoclass:: TryExceptMultipleReturnPathViolation


from wemake_python_styleguide.types import final
from wemake_python_styleguide.violations.base import (

[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`` 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 check this count on a per-module basis. We use :str:`wemake_python_styleguide.constants.MAX_NOQA_COMMENTS` as a default value. Reasoning: Having too many ``# noqa`` comments with make your code less readable and clearly indicates that there's something wrong with it. Solution: Refactor your code to much the style. Or use a config file to switch off some checks. .. versionadded:: 0.7.0 """ error_template = 'Found `noqa` comments overuse: {0}' code = 402
# Modules:
[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.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``. Default: :str:`wemake_python_styleguide.options.defaults.I_CONTROL_CODE` .. versionadded:: 0.1.0 """ error_template = 'Found `` module with logic' code = 412
# Modules:
[docs]@final class WrongKeywordViolation(ASTViolation): """ Forbids to use some keywords from ``python``. Reasoning: We believe that some keywords are anti-patterns. They promote bad-practices like ``global`` and ``pass``, or just not user-friendly like ``del``. 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. Example:: # Wrong: pass del nonlocal global .. 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: .. 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: """ 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: """ 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
# Design:
[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). See :py:data:`~wemake_python_styleguide.constants.NESTED_CLASSES_WHITELIST` for the full list of whitelisted names. Example:: # Correct: class Some(object): ... class Other(object): ... # Wrong: class Some(object): class Inner(object): ... .. versionadded:: 0.1.0 """ 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: """ code = 432 error_template = 'Found magic number: {0}'
[docs]@final class StaticMethodViolation(ASTViolation): """ Forbids to use ``@staticmethod`` decorator. Reasoning: Static methods are not required to be inside the class. Because they even do not have access to the current instance. Solution: Use instance methods, ``@classmethod``, or functions instead. .. versionadded:: 0.1.0 """ error_template = 'Found using `@staticmethod`' code = 433
[docs]@final class BadMagicMethodViolation(ASTViolation): """ Forbids to use some magic methods. Reasoning: We forbid to use magic methods related to the forbidden language parts. Likewise, we forbid to use ``del`` keyword, so we forbid to use all magic methods related to it. Solution: Refactor your code to use custom methods instead. It will give more context to your app. See :py:data:`~wemake_python_styleguide.constants.MAGIC_METHODS_BLACKLIST` for the full blacklist of the magic methods. .. versionadded:: 0.1.0 See also: """ error_template = 'Found using restricted magic method: {0}' code = 434
[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 See also: """ error_template = 'Found nested import' code = 435
[docs]@final class RedundantLoopElseViolation(ASTViolation): """ Forbids to use ``else`` without ``break`` in a loop. We use the same logic for ``for`` and ``while`` loops. Reasoning: When there's no ``break`` keyword in loop's body it means that ``else`` will always be called. This rule will reduce complexity, improve readability, and protect from possible errors. Solution: Refactor your ``else`` case logic to be inside the loop's body. Or right after it. Example:: # Correct: for letter in 'abc': if letter == 'b': break else: print('"b" is not found') for letter in 'abc': print(letter) print('always called') # Wrong: for letter in 'abc': print(letter) else: print('always called') .. versionadded:: 0.3.0 """ error_template = 'Found `else` in a loop without `break`' code = 436
[docs]@final class RedundantFinallyViolation(ASTViolation): """ Forbids to use ``finally`` in ``try`` block without ``except`` block. Reasoning: This rule will reduce complexity and improve readability. Solution: Refactor your ``try`` logic. Replace the ``try-finally`` statement with a ``with`` statement. Example:: # Correct: with open("filename") as f: f.write(...) # Wrong: try: f = open("filename") f.write(...) finally: f.close() .. versionadded:: 0.3.0 """ error_template = 'Found `finally` in `try` block without `except`' code = 437
[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 """ error_template = 'Found reassigning variable to itself' code = 438
[docs]@final class YieldInsideInitViolation(ASTViolation): """ Forbids to use ``yield`` inside of ``__init__`` method. Reasoning: ``__init__`` should be used to initialize new objects. It shouldn't ``yield`` anything because it should return ``None`` by the convention. Example:: # Correct: class Example(object): def __init__(self): self._public_items_count = 0 # Wrong: class Example(object): def __init__(self): yield 10 .. versionadded:: 0.3.0 """ error_template = 'Found `yield` inside `__init__` method' code = 439
[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 """ error_template = 'Found protected module import' code = 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() # Wrong: print(some._protected) instance._hidden() self.container._internal = 10 Note, that it is possible to use protected attributes with ``self`` and ``cls`` 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 """ error_template = 'Found protected attribute usage: {0}' code = 441
[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 See also: """ error_template = "Found `lambda` in loop's body" code = 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 """ error_template = 'Found unreachable code' code = 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 """ error_template = 'Found statement that has no effect' code = 444
[docs]@final class MultipleAssignmentsViolation(ASTViolation): """ Forbids to have statements that do nothing. 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 """ error_template = 'Found multiple assign targets' code = 445
[docs]@final class IncorrectUnpackingViolation(ASTViolation): """ Forbids to have statements that do nothing. 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 """ error_template = 'Found incorrect unpacking target' code = 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 """ error_template = 'Found duplicate exception: {0}' code = 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') ['a', None, 'b', None] >>> list([(yield letter) for letter in 'ab']) ['a', 'b'] See also: .. versionadded:: 0.7.0 """ error_template = 'Found `yield` inside comprehension' code = 448
[docs]@final class NonUniqueItemsInSetViolation(ASTViolation): """ Forbids to have duplicate items in ``set`` literals. Reasoning: When you explicitly put duplicate items in ``set`` literals it just does not make any sense. Since ``set`` can not contain duplicate items and they will be removed anyway. Solution: Remove the 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 - containers: lists, dicts, tuples, sets .. versionadded:: 0.7.0 """ error_template = 'Found non-unique item in `set` literal: {0}' code = 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: .. versionadded:: 0.7.0 """ error_template = 'Found exception inherited from `BaseException`' code = 450
[docs]@final class SimplifiableIfViolation(ASTViolation): """ Forbids to have simplifiable ``if`` conditions. Reasoning: This complex construction can cause frustration among other developers. It is longer, more verbose, and more complex. Solution: Use ``bool()`` to convert test values to boolean values. Or just leave it as it is in case when your test already returns a boolean value. Use can also use ``not`` keyword to switch boolean values. Example:: # Correct: my_bool = bool(some_call()) other_value = 8 if some_call() else None # Wrong: my_bool = True if some_call() else False We only check ``if`` nodes where ``True`` and ``False`` values are used. We check both ``if`` nodes and ``if`` expressions. .. versionadded:: 0.7.0 """ error_template = 'Found simplifiable `if` condition' code = 451
[docs]@final class IncorrectClassBodyContentViolation(ASTViolation): """ Forbids to use incorrect nodes inside ``class`` definitions. Reasoning: Python allows us to have conditions, context managers, and even infinite loops inside ``class`` definitions. On the other hand, only methods, attributes, and docstrings make sense. So, we discourage using anything except these nodes in class bodies. Solution: If you have complex logic inside your class definition, most likely that you do something wrong. There are different options to refactor this mess. You can try metaclasses, decorators, builders, and other patterns. Example:: # Wrong: class Test(object): for _ in range(10): print('What?!') We also allow some nested classes, check out :class:`NestedClassViolation` for more information. .. versionadded:: 0.7.0 """ error_template = 'Found incorrect node inside `class` body' code = 452
[docs]@final class MethodWithoutArgumentsViolation(ASTViolation): """ Forbids to have methods without any arguments. Reasoning: Methods withour arguments are allowed to be defined, but almost impossible to use. Furthermore, they don't have an access to ``self``, so can not access the inner state of the object. It might be an intentional design or just a typo. Solution: Move any methods with arguments to raw functions. Or just add an argument if it is actually required. Example:: # Correct: class Test(object): def method(self): ... # Wrong: class Test(object): def method(): ... .. versionadded:: 0.7.0 """ error_template = 'Found method without arguments: {0}' code = 453
[docs]@final class IncorrectBaseClassViolation(ASTViolation): """ Forbids to have methods without any arguments. Reasoning: In Python you can specify anything in the base classes slot. In runtime this expression will be evaluated and executed. We need to prevent dirty hacks in this field. Solution: Use only attributes, names, and types to be your base classes. Example:: # Correct: class Test(module.ObjectName, MixinName, keyword=True): ... class GenericClass(Generic[ValueType]): ... # Wrong: class Test((lambda: object)()): ... .. versionadded:: 0.7.0 .. versionchanged:: 0.7.1 """ error_template = 'Found incorrect base class' code = 454
[docs]@final class IncorrectSlotsViolation(ASTViolation): """ Forbids to have incorrect ``__slots__`` definition. Reasoning: ``__slots__`` is a very special attribute. It completely changes your class. So, we need to be careful with it. We should not allow anything rather than tuples to define slots, we also need to check that fields defined in ``__slots__`` are unique. Solution: Use tuples with unique elements to define ``__slots__`` attribute. Example:: # Correct: class Test(object): __slots__ = ('field1', 'field2') class Other(Test): __slots__ = Test.__slots__ + ('child',) # Wrong: class Test(object): __slots__ = ['field1', 'field2', 'field2'] Note, that we do ignore all complex expressions for this field. So, we only check raw literals. .. versionadded:: 0.7.0 """ error_template = 'Found incorrect `__slots__` syntax' code = 455
[docs]@final class IncorrectSuperCallViolation(ASTViolation): """ Forbids to use ``super()`` with parameters or outside of methods. Reasoning: ``super()`` is a very special function. It implicitly relies on the context where it is used and parameters passed to it. So, we should be very careful with parameters and context. Solution: Use ``super()`` without arguments and only inside methods. Example:: # Correct: super().__init__() # Wrong: super(ClassName, self).__init__() .. versionadded:: 0.7.0 """ error_template = 'Found incorrect `super()` call: {0}' code = 456
[docs]@final class RedundantReturningElseViolation(ASTViolation): """ Forbids to use redundant ``else`` cases in returning functions. We check single ``if`` statements that all contain ``return`` or ``raise`` or ``break`` statements with this rule. We do not check ``if`` statements with ``elif`` cases. Reasoning: Using extra ``else`` creates a situation when the whole node could and should be dropped without any changes in logic. So, we prefer to have less code than more code. Solution: Remove redundant ``else`` case. Example:: # Correct: def some_function(): if some_call(): return 'yeap' return 'nope' # Wrong: def some_function(): if some_call(): raise ValueError('yeap') else: raise ValueError('nope') .. versionadded:: 0.7.0 """ error_template = 'Found redundant returning `else` statement' code = 457
[docs]@final class TryExceptMultipleReturnPathViolation(ASTViolation): """ Forbids to use multiple ``return`` path with ``try`` / ``except`` case. 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:: # 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 """ error_template = 'Found `try`/`else`/`finally` with multiple return paths' code = 458