Which is not base in the following?

Sodium hydroxide, calcium carbonate and potassium oxide are examples of bases. A base is a material that interacts with hydrogen ions and can neutralize the acid. Bases are classified as acceptors of a proton (H+). Metal oxides and metal hydroxides and ammonium hydroxide are typical examples of the bases.

The from abc import ABCMeta class MyABC(metaclass=ABCMeta): pass 3 module has some concrete classes that derive from ABCs; these can, of course, be further derived. In addition, the from abc import ABCMeta class MyABC(metaclass=ABCMeta): pass 4 submodule has some ABCs that can be used to test whether a class or instance provides a particular interface, for example, if it is hashable or if it is a mapping.

This module provides the metaclass from abc import ABCMeta class MyABC(metaclass=ABCMeta): pass 5 for defining ABCs and a helper class from abc import ABCMeta class MyABC(metaclass=ABCMeta): pass 6 to alternatively define ABCs through inheritance:

A helper class that has from abc import ABCMeta class MyABC(metaclass=ABCMeta): pass 5 as its metaclass. With this class, an abstract base class can be created by simply deriving from from abc import ABCMeta class MyABC(metaclass=ABCMeta): pass 6 avoiding sometimes confusing metaclass usage, for example:

from abc import ABC class MyABC(ABC): pass

Note that the type of from abc import ABCMeta class MyABC(metaclass=ABCMeta): pass 6 is still from abc import ABCMeta class MyABC(metaclass=ABCMeta): pass 5, therefore inheriting from from abc import ABCMeta class MyABC(metaclass=ABCMeta): pass 6 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 from abc import ABCMeta class MyABC(metaclass=ABCMeta): pass 5 directly, for example:

from abc import ABCMeta class MyABC(metaclass=ABCMeta): pass

New in version 3.4.

Metaclass for defining Abstract Base Classes (ABCs).

Use this metaclass to create an ABC. An ABC can be subclassed directly, and then acts as a mix-in class. You can also register unrelated concrete classes (even built-in classes) and unrelated ABCs as “virtual subclasses” – these and their descendants will be considered subclasses of the registering ABC by the built-in from abc import ABC class MyABC(ABC): pass MyABC.register(tuple) assert issubclass(tuple, MyABC) assert isinstance((), MyABC) 3 function, but the registering ABC won’t show up in their MRO (Method Resolution Order) nor will method implementations defined by the registering ABC be callable (not even via from abc import ABC class MyABC(ABC): pass MyABC.register(tuple) assert issubclass(tuple, MyABC) assert isinstance((), MyABC) 4). 1

Classes created with a metaclass of from abc import ABCMeta class MyABC(metaclass=ABCMeta): pass 5 have the following method:

Register subclass as a “virtual subclass” of this ABC. For example:

from abc import ABC class MyABC(ABC): pass MyABC.register(tuple) assert issubclass(tuple, MyABC) assert isinstance((), MyABC)

Changed in version 3.3: Returns the registered subclass, to allow usage as a class decorator.

Changed in version 3.4: To detect calls to from abc import ABC class MyABC(ABC): pass MyABC.register(tuple) assert issubclass(tuple, MyABC) assert isinstance((), MyABC) 6, you can use the from abc import ABC class MyABC(ABC): pass MyABC.register(tuple) assert issubclass(tuple, MyABC) assert isinstance((), MyABC) 7 function.

You can also override this method in an abstract base class:

(Must be defined as a class method.)

Check whether subclass is considered a subclass of this ABC. This means that you can customize the behavior of from abc import ABC class MyABC(ABC): pass MyABC.register(tuple) assert issubclass(tuple, MyABC) assert isinstance((), MyABC) 8 further without the need to call from abc import ABC class MyABC(ABC): pass MyABC.register(tuple) assert issubclass(tuple, MyABC) assert isinstance((), MyABC) 6 on every class you want to consider a subclass of the ABC. (This class method is called from the 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) 0 method of the ABC.)

This method should return 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) 1, 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) 2 or 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) 3. If it returns 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) 1, the subclass is considered a subclass of this ABC. If it returns 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) 2, the subclass is not considered a subclass of this ABC, even if it would normally be one. If it returns 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) 3, the subclass check is continued with the usual mechanism.

For a demonstration of these concepts, look at this example ABC definition:

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)

The ABC 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) 7 defines the standard iterable method, 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) 8, as an abstract method. The implementation given here can still be called from subclasses. The 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) 9 method is also part of the 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) 7 abstract base class, but it does not have to be overridden in non-abstract derived classes.

The 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) 1 class method defined here says that any class that has an 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) 8 method in its 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) 3 (or in that of one of its base classes, accessed via the 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) 4 list) is considered a 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) 7 too.

Finally, the last line makes 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) 6 a virtual subclass of 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) 7, even though it does not define an 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) 8 method (it uses the old-style iterable protocol, defined in terms of 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) 9 and class Descriptor: ... @property def __isabstractmethod__(self): return any(getattr(f, '__isabstractmethod__', False) for f in (self._fget, self._fset, self._fdel)) 0). Note that this will not make class Descriptor: ... @property def __isabstractmethod__(self): return any(getattr(f, '__isabstractmethod__', False) for f in (self._fget, self._fset, self._fdel)) 1 available as a method of 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) 6, so it is provided separately.

The from abc import ABCMeta class MyABC(metaclass=ABCMeta): pass 1 module also provides the following decorator:

A decorator indicating abstract methods.

Using this decorator requires that the class’s metaclass is from abc import ABCMeta class MyABC(metaclass=ABCMeta): pass 5 or is derived from it. A class that has a metaclass derived from from abc import ABCMeta class MyABC(metaclass=ABCMeta): pass 5 cannot be instantiated unless all of its abstract methods and properties are overridden. The abstract methods can be called using any of the normal ‘super’ call mechanisms. class Descriptor: ... @property def __isabstractmethod__(self): return any(getattr(f, '__isabstractmethod__', False) for f in (self._fget, self._fset, self._fdel)) 6 may be used to declare abstract methods for properties and descriptors.

Dynamically adding abstract methods to a class, or attempting to modify the abstraction status of a method or class once it is created, are only supported using the class Descriptor: ... @property def __isabstractmethod__(self): return any(getattr(f, '__isabstractmethod__', False) for f in (self._fget, self._fset, self._fdel)) 7 function. The class Descriptor: ... @property def __isabstractmethod__(self): return any(getattr(f, '__isabstractmethod__', False) for f in (self._fget, self._fset, self._fdel)) 6 only affects subclasses derived using regular inheritance; “virtual subclasses” registered with the ABC’s from abc import ABC class MyABC(ABC): pass MyABC.register(tuple) assert issubclass(tuple, MyABC) assert isinstance((), MyABC) 6 method are not affected.

When class Descriptor: ... @property def __isabstractmethod__(self): return any(getattr(f, '__isabstractmethod__', False) for f in (self._fget, self._fset, self._fdel)) 6 is applied in combination with other method descriptors, it should be applied as the innermost decorator, as shown in the following usage examples:

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)

In order to correctly interoperate with the abstract base class machinery, the descriptor must identify itself as abstract using class C(ABC): @classmethod @abstractmethod def my_abstract_classmethod(cls, arg): ... 1. In general, this attribute should be 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) 1 if any of the methods used to compose the descriptor are abstract. For example, Python’s built-in class C(ABC): @classmethod @abstractmethod def my_abstract_classmethod(cls, arg): ... 3 does the equivalent of:

class Descriptor: ... @property def __isabstractmethod__(self): return any(getattr(f, '__isabstractmethod__', False) for f in (self._fget, self._fset, self._fdel))

Note

Unlike Java abstract methods, these abstract methods may have an implementation. This implementation can be called via the from abc import ABC class MyABC(ABC): pass MyABC.register(tuple) assert issubclass(tuple, MyABC) assert isinstance((), MyABC) 4 mechanism from the class that overrides it. This could be useful as an end-point for a super-call in a framework that uses cooperative multiple-inheritance.

The from abc import ABCMeta class MyABC(metaclass=ABCMeta): pass 1 module also supports the following legacy decorators:

New in version 3.2.

Deprecated since version 3.3: It is now possible to use class C(ABC): @classmethod @abstractmethod def my_abstract_classmethod(cls, arg): ... 6 with class Descriptor: ... @property def __isabstractmethod__(self): return any(getattr(f, '__isabstractmethod__', False) for f in (self._fget, self._fset, self._fdel)) 6, making this decorator redundant.

A subclass of the built-in class C(ABC): @classmethod @abstractmethod def my_abstract_classmethod(cls, arg): ... 8, indicating an abstract classmethod. Otherwise it is similar to class Descriptor: ... @property def __isabstractmethod__(self): return any(getattr(f, '__isabstractmethod__', False) for f in (self._fget, self._fset, self._fdel)) 6.

This special case is deprecated, as the class C(ABC): @classmethod @abstractmethod def my_abstract_classmethod(cls, arg): ... 8 decorator is now correctly identified as abstract when applied to an abstract method:

class C(ABC): @classmethod @abstractmethod def my_abstract_classmethod(cls, arg): ...

New in version 3.2.

Deprecated since version 3.3: It is now possible to use class C(ABC): @staticmethod @abstractmethod def my_abstract_staticmethod(arg): ... 1 with class Descriptor: ... @property def __isabstractmethod__(self): return any(getattr(f, '__isabstractmethod__', False) for f in (self._fget, self._fset, self._fdel)) 6, making this decorator redundant.

A subclass of the built-in class C(ABC): @staticmethod @abstractmethod def my_abstract_staticmethod(arg): ... 3, indicating an abstract staticmethod. Otherwise it is similar to class Descriptor: ... @property def __isabstractmethod__(self): return any(getattr(f, '__isabstractmethod__', False) for f in (self._fget, self._fset, self._fdel)) 6.

This special case is deprecated, as the class C(ABC): @staticmethod @abstractmethod def my_abstract_staticmethod(arg): ... 3 decorator is now correctly identified as abstract when applied to an abstract method:

class C(ABC): @staticmethod @abstractmethod def my_abstract_staticmethod(arg): ...

Deprecated since version 3.3: It is now possible to use class C(ABC): @classmethod @abstractmethod def my_abstract_classmethod(cls, arg): ... 3, class C(ABC): @staticmethod @abstractmethod def my_abstract_staticmethod(arg): ... 7, class C(ABC): @staticmethod @abstractmethod def my_abstract_staticmethod(arg): ... 8 and class C(ABC): @staticmethod @abstractmethod def my_abstract_staticmethod(arg): ... 9 with class Descriptor: ... @property def __isabstractmethod__(self): return any(getattr(f, '__isabstractmethod__', False) for f in (self._fget, self._fset, self._fdel)) 6, making this decorator redundant.

A subclass of the built-in class C(ABC): @property @abstractmethod def my_abstract_property(self): ... 1, indicating an abstract property.

This special case is deprecated, as the class C(ABC): @property @abstractmethod def my_abstract_property(self): ... 1 decorator is now correctly identified as abstract when applied to an abstract method:

class C(ABC): @property @abstractmethod def my_abstract_property(self): ...

The above example defines a read-only property; you can also define a read-write abstract property by appropriately marking one or more of the underlying methods as abstract:

class C(ABC): @property def x(self): ... @x.setter @abstractmethod def x(self, val): ...

If only some components are abstract, only those components need to be updated to create a concrete property in a subclass:

from abc import ABCMeta class MyABC(metaclass=ABCMeta): pass 0

The from abc import ABCMeta class MyABC(metaclass=ABCMeta): pass 1 module also provides the following functions:

Returns the current abstract base class cache token.

The token is an opaque object (that supports equality testing) identifying the current version of the abstract base class cache for virtual subclasses. The token changes with every call to class C(ABC): @property @abstractmethod def my_abstract_property(self): ... 4 on any ABC.

New in version 3.4.

A function to recalculate an abstract class’s abstraction status. This function should be called if a class’s abstract methods have been implemented or changed after it was created. Usually, this function should be called from within a class decorator.

Returns cls, to allow usage as a class decorator.

If cls is not an instance of from abc import ABCMeta class MyABC(metaclass=ABCMeta): pass 5, does nothing.

Note

This function assumes that cls’s superclasses are already updated. It does not update any subclasses.

Which of the following is not a base?

Which is the following is a base?

Which is a base or not?

What are the 5 types of base?