A. Configure the python checker to call a Python 3 interpreter rather than Python 2, e.g:
let g: syntastic_python_python_exec = '/path/to/python3'
Emitted whenever we can detect that a class is using, as a metaclass, something which might be invalid for using as a metaclass.,old-deprecated-class/W1512Toggle child pages in navigation deprecated-class / W4904 ,Technical ReferenceToggle child pages in navigation Startup and the Linter Class Checkers ,lru-cache-decorating-method/W1516Toggle child pages in navigation method-cache-max-size-none / W1518
# This is a placeholder for correct code for this message.
The easiest way to ensure that Pylint uses the desired .pylintrc file is to place it in the same working directory as your code. Open the file into an editor to take a look at the configuration options. , Pylint is an excellent tool to have good quality code. This post is not about how pylint works. Lets see most common pylint errors: When you are defining methods in python, its necessary to give them some text help what the function is all about. ,i try to fix all pylint errors and pylint warnings in a project. but i keep getting an error when i set a metaclass (https://www.python.org/dev/peps/pep-3115/)., 3 days ago Aug 23, 2019 · Errors: line too long, trailing whitespace, wrong import order. Now that you've resolved the syntax error, Pylint has found three linting errors. pylint_example.py 15: Line too long (106/100) (line-too-long) Line 15 is too long. In this case, there doesn't need to be much more explanation, so Pylint keeps it simple.
#!/usr/bin/env python3 class MyMeta(type): pass class MyObject(object, metaclass=MyMeta): # pylint error here pass
let g: syntastic_python_python_exec = '/path/to/python3'
A helper class that has ABCMeta as its metaclass. With this class, an abstract base class can be created by simply deriving from ABC avoiding sometimes confusing metaclass usage, for example:,Note that the type of ABC is still ABCMeta, therefore inheriting from ABC requires the usual precautions regarding metaclass usage, as multiple inheritance may lead to metaclass conflicts. One may also define an abstract base class by passing the metaclass keyword and using ABCMeta directly, for example:,This module provides the metaclass ABCMeta for defining ABCs and a helper class ABC to alternatively define ABCs through inheritance:,The __subclasshook__() class method defined here says that any class that has an __iter__() method in its __dict__ (or in that of one of its base classes, accessed via the __mro__ list) is considered a MyIterable too.
from abc import ABC class MyABC(ABC): pass
from abc import ABCMeta class MyABC(metaclass = ABCMeta): pass
from abc import ABC class MyABC(ABC): pass MyABC.register(tuple) assert issubclass(tuple, MyABC) assert isinstance((), MyABC)
class Foo: def __getitem__(self, index): ... def __len__(self): ... def get_iterator(self): return iter(self) class MyIterable(ABC): @abstractmethod def __iter__(self): while False: yield None def get_iterator(self): return self.__iter__() @classmethod def __subclasshook__(cls, C): if cls is MyIterable: if any("__iter__" in B.__dict__ for B in C.__mro__): return True return NotImplemented MyIterable.register(Foo)
class C(ABC): @abstractmethod def my_abstract_method(self, arg1): ... @classmethod @abstractmethod def my_abstract_classmethod(cls, arg2): ... @staticmethod @abstractmethod def my_abstract_staticmethod(arg3): ... @property @abstractmethod def my_abstract_property(self): ... @my_abstract_property.setter @abstractmethod def my_abstract_property(self, val): ... @abstractmethod def _get_x(self): ... @abstractmethod def _set_x(self, val): ... x = property(_get_x, _set_x)
class Descriptor: ... @property def __isabstractmethod__(self): return any(getattr(f, '__isabstractmethod__', False) for f in (self._fget, self._fset, self._fdel))
A metaclass is a class that describes the construction and behavior of other classes, similarly to how classes describe the construction and behavior of objects. The default metaclass is type, but it’s possible to use other metaclasses. Metaclasses allows one to create “a different kind of class”, such as Enums, NamedTuples and singletons.,Note that metaclasses pose some requirements on the inheritance structure, so it’s better not to combine metaclasses and class hierarchies:,Mypy does not understand dynamically-computed metaclasses, such as class A(metaclass=f()): ...,Metaclasses Defining a metaclass Metaclass usage example Gotchas and limitations of metaclass support
class M(type): pass class A(metaclass = M): pass
class A(object): __metaclass__ = M
import six class A(six.with_metaclass(M)): pass @six.add_metaclass(M) class C(object): pass
from typing import Type, TypeVar, ClassVar T = TypeVar('T') class M(type): count: ClassVar[int] = 0 def make(cls: Type[T]) - > T: M.count += 1 return cls() class A(metaclass = M): pass a: A = A.make() # make() is looked up at M; the result is an object of type A print(A.count) class B(A): pass b: B = B.make() # metaclasses are inherited print(B.count + " objects were created") # Error: Unsupported operand types for +("int" and "str")
class M1(type): pass class M2(type): pass class A1(metaclass = M1): pass class A2(metaclass = M2): pass class B1(A1, metaclass = M2): pass # Mypy Error: Inconsistent metaclass structure for "B1" # At runtime the above definition raises an exception # TypeError: metaclass conflict: the metaclass of a derived class must be a(non - strict) subclass of the metaclasses of all its bases # Same runtime error as in B1, but mypy does not catch it yet class B12(A1, A2): pass
The class in Python is also an object, and therefore, like other objects, it is an instance of Metaclass. The metaclass is a special class type which is responsible for creating classes and Class object. So, for example, if the user wants to find the type of the "City" class, they will find out that it is "type.",As the classes are also an object, we can modify them. For example, the user can add or subtract fields or functions in the class as we do with other objects.,Metaclass is used for creating Classes, and these classes can create the objects.,As shown in the above example, Metaclass is used for generating down the inheritance hierarchies. This will affect all the subclasses also. If the user has such situations, then they can use the metaclass.
Type of number is: <class 'int'> Type of list is: <class 'list'> Type of name is: <class 'str'>
Type of City_object is: <class '__main__.City'>
Type of City class is: <class 'type'>
The Type of City class: <class 'type'> The Type of City_object: <class '__main__.City'> This is a inherited method! This is City class method! Mark Jackson
--------------------------------------------------------------------------- TypeError Traceback (most recent call last) <ipython-input-2-409c90c285d5> in <module> 29 pass 30 # This will raise an error! ---> 31 class S(P, Q, R): 32 pass <ipython-input-2-409c90c285d5> in __new__(city, city_name, bases, citydict) 6 # it will raise an error 7 if len(bases)>1: ----> 8 raise TypeError("There are inherited multiple base classes!!!") 9 10 # else it will execute the __new__() function of super class, that is TypeError: There are inherited multiple base classes!!!
Error codes with [+] mean they’ve got examples of bad and good code. Rationalisation provided for all entries.,It’s not required to install CLI util as long as you can navigate list of errors here or on this web-site but you may want to do so.,In order to get the latest updates just git pull origin master and invoke a command in the root of the project (sudo apt install make if not yet installed) make rai to install to Python 3 user space site packages or make raip for pipx.,In order to use development plerr builds you need to invoke the following commands:
$ python3 - m pip install plerr $ plerr r1710
$ python3 - m pip install pipx # if not yet installed pipx $ python3 - m pipx ensurepath # ensure directory where pipx stores apps is on PATH $ pipx install plerr $ plerr r1710
$ git clone https: //github.com/vald-phoenix/pylint-errors.git $ sudo apt update && sudo apt install - y python3 - pip # if not yet installed $ cd pylint - errors $ python3 setup.py test $ python3 setup.py install--user $ python3 - m plerr r1710
$ git clone https: //github.com/vald-phoenix/pylint-errors.git $ sudo apt install - y make python3 - pip python3 - venv # if not yet installed $ cd pylint - errors $ python3 - m pip install pipx wheel # install a package to build a wheel and pipx $ python3 - m pipx ensurepath # ensure directory where pipx stores apps is on PATH $ python3 setup.py test # run tests $ make clean $ python3 setup.py bdist_wheel # build a binary wheel $ pipx install dist /* # install a binary wheel by pipx $ plerr r1710