OOP¶
These checks ensures that you use Python’s version of OOP correctly.
There are different gotchas in Python to write beatiful classes and using objects correctly. That’s the place we collect these kind of rules.
Summary¶
Forbids to subclass lowercase builtins. |
|
Forbids to shadow class level attributes with instance level attributes. |
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Forbids to use |
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Forbids to use some magic methods. |
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Forbids to use incorrect nodes inside |
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Forbids to have methods without any arguments. |
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Forbids to have anything else than a class as a base class. |
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Forbids to have incorrect |
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Forbids to use |
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Forbids to use direct magic attributes and methods. |
|
Forbids to make some magic methods async. |
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Forbids to use |
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Forbids to have useless overwritten methods. |
Respect your objects¶
-
class
BuiltinSubclassViolation
(node, text=None)[source]¶ Bases:
wemake_python_styleguide.violations.base.ASTViolation
Forbids to subclass lowercase builtins.
We forbid to subclass builtins like
int
,str
,bool
, etc. We allow to subclassobject
andtype
, warnings, and exceptions.See
ALLOWED_BUILTIN_CLASSES
for the whole list of whitelisted names.- Reasoning:
It is almost never a good idea (unless you do something sneaky) to subclass primitive builtins.
- Solution:
Use custom objects around some wrapper. Use magic methods to emulate the desired behaviour.
Example:
# Correct: class Some(object): ... class MyValueException(ValueError): ... # Wrong: class MyInt(int): ...
New in version 0.10.0.
Changed in version 0.11.0.
-
error_template
= 'Found subclassing a builtin: {0}'¶
-
code
= 600¶
-
previous_codes
= {426}¶
-
class
ShadowedClassAttributeViolation
(node, text=None)[source]¶ Bases:
wemake_python_styleguide.violations.base.ASTViolation
Forbids to shadow class level attributes with instance level attributes.
- Reasoning:
This way you will have two attributes inside your
__mro__
chain: one from instance and one from class. It might cause errors. Needless to say, that this is just pointless to do so.- Solution:
Use either class attributes or instance attributes. Use
ClassVar
type on fields that are declared as class attributes.
Note, that we cannot find shadowed attributes that are defined in parent classes. That’s where
ClassVar
is required formypy
to check it for you.Example:
# Correct: from typing import ClassVar class First(object): field: ClassVar[int] = 1 class Second(object): field: int def __init__(self) -> None: self.field = 1 # Wrong: class Some(object): field = 1 def __init__(self) -> None: self.field = 1
New in version 0.10.0.
Changed in version 0.11.0.
-
error_template
= 'Found shadowed class attribute: {0}'¶
-
code
= 601¶
-
previous_codes
= {427}¶
-
class
StaticMethodViolation
(node, text=None)[source]¶ Bases:
wemake_python_styleguide.violations.base.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.
New in version 0.1.0.
Changed in version 0.11.0.
-
error_template
= 'Found using `@staticmethod`'¶
-
code
= 602¶
-
previous_codes
= {433}¶
-
class
BadMagicMethodViolation
(node, text=None)[source]¶ Bases:
wemake_python_styleguide.violations.base.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
MAGIC_METHODS_BLACKLIST
for the full blacklist of the magic methods.New in version 0.1.0.
Changed in version 0.11.0.
-
error_template
= 'Found using restricted magic method: {0}'¶
-
code
= 603¶
-
previous_codes
= {434}¶
-
class
WrongClassBodyContentViolation
(node, text=None)[source]¶ Bases:
wemake_python_styleguide.violations.base.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
NestedClassViolation
for more information.New in version 0.7.0.
Changed in version 0.11.0.
-
error_template
= 'Found incorrect node inside `class` body'¶
-
code
= 604¶
-
previous_codes
= {452}¶
-
class
MethodWithoutArgumentsViolation
(node, text=None)[source]¶ Bases:
wemake_python_styleguide.violations.base.ASTViolation
Forbids to have methods without any arguments.
- Reasoning:
Methods without 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(): ...
New in version 0.7.0.
Changed in version 0.11.0.
-
error_template
= 'Found method without arguments: {0}'¶
-
code
= 605¶
-
previous_codes
= {453}¶
-
class
WrongBaseClassViolation
(node, text=None)[source]¶ Bases:
wemake_python_styleguide.violations.base.ASTViolation
Forbids to have anything else than a class as a base class.
We only check base classes and not keywords. They can be anything you need.
- 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. Use
annotation
future import in case you use strings in base classes.
Example:
# Correct: class Test(module.ObjectName, MixinName, keyword=True): ... class GenericClass(Generic[ValueType]): ... # Wrong: class Test((lambda: object)()): ...
New in version 0.7.0.
Changed in version 0.7.1.
Changed in version 0.11.0.
Changed in version 0.12.0.
-
error_template
= 'Found incorrect base class'¶
-
code
= 606¶
-
previous_codes
= {454}¶
-
class
WrongSlotsViolation
(node, text=None)[source]¶ Bases:
wemake_python_styleguide.violations.base.ASTViolation
Forbids to have incorrect
__slots__
definition.Things that this rule checks:
That
__slots__
is a tuple, name, attribute, star, or callThat
__slots__
do not have duplicatesThat
__slots__
do not have empty strings or invalid python names
- 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. Usesnake_case
to define attributes in__slots__
.
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.
New in version 0.7.0.
Changed in version 0.11.0.
Changed in version 0.12.0.
-
error_template
= 'Found incorrect `__slots__` syntax'¶
-
code
= 607¶
-
previous_codes
= {455}¶
-
class
WrongSuperCallViolation
(node, text=None)[source]¶ Bases:
wemake_python_styleguide.violations.base.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__()
New in version 0.7.0.
Changed in version 0.11.0.
-
error_template
= 'Found incorrect `super()` call: {0}'¶
-
code
= 608¶
-
previous_codes
= {456}¶
-
class
DirectMagicAttributeAccessViolation
(node, text=None)[source]¶ Bases:
wemake_python_styleguide.violations.base.ASTViolation
Forbids to use direct magic attributes and methods.
- Reasoning:
When using direct magic attributes or method it means that you are doing something wrong. Magic methods are not suited to be directly called or accessed.
- Solution:
Use special syntax constructs that will call underlying magic methods.
Example:
# Correct: super().__init__() # Wrong: 2..__truediv__(2) d.__delitem__('a')
Note, that it is possible to use direct magic attributes with
self
,cls
, andsuper()
as base names. We allow this because a lot of internal logic relies on these methods.New in version 0.8.0.
Changed in version 0.11.0.
-
error_template
= 'Found direct magic attribute usage: {0}'¶
-
code
= 609¶
-
previous_codes
= {462}¶
-
class
AsyncMagicMethodViolation
(node, text=None)[source]¶ Bases:
wemake_python_styleguide.violations.base.ASTViolation
Forbids to make some magic methods async.
We allow to make
__anext__
,__aenter__
,__aexit__
async. We also allow custom magic methods to be async.See
ASYNC_MAGIC_METHODS_BLACKLIST
for the whole list of blacklisted async magic methods.- Reasoning:
Defining the magic methods as async which are not supposed to be async would not work as expected.
- Solution:
Do not make this magic method async.
Example:
# Correct: class Test(object): def __lt__(self, other): ... # Wrong: class Test(object): async def __lt__(self, other): ...
New in version 0.12.0.
-
error_template
= 'Found forbidden `async` magic method usage: {0}'¶
-
code
= 610¶
-
class
YieldMagicMethodViolation
(node, text=None)[source]¶ Bases:
wemake_python_styleguide.violations.base.ASTViolation
Forbids to use
yield
inside of several magic methods.We allow to make
__iter__
a generator. SeeYIELD_MAGIC_METHODS_BLACKLIST
for the whole list of blacklisted generator magic methods.- Reasoning:
Python’s datamodel is strict. You cannot make generators from random magic methods. This rule enforces it.
- Solution:
Remove
yield
from a magic method or rename it to be a custom method.
Example:
# Correct: class Example(object): def __init__(self): ... # Wrong: class Example(object): def __init__(self): yield 10
New in version 0.3.0.
Changed in version 0.11.0.
Changed in version 0.12.0.
-
error_template
= 'Found forbidden `yield` magic method usage'¶
-
code
= 611¶
-
previous_codes
= {435, 439}¶
-
class
UselessOverwrittenMethodViolation
(node, text=None)[source]¶ Bases:
wemake_python_styleguide.violations.base.ASTViolation
Forbids to have useless overwritten methods.
- Reasoning:
Overwriting method without any changes does not have any positive impact.
- Solution:
Do not overwrite method in case you do not want to do any changes inside it.
Example:
# Correct: class Test(Base): ... # Wrong: class Test(object): def method(self, argument): return super().method(argument)
New in version 0.12.0.
-
error_template
= 'Found useless overwritten method: {0}'¶
-
code
= 612¶