"abc" --- abstrakcyjne klasy bazowe
***********************************

**Kod źródłowy:**. Lib/abc.py

======================================================================

This module provides the infrastructure for defining *abstract base
classes* (ABCs) in Python, as outlined in **PEP 3119**; see the PEP
for why this was added to Python. (See also **PEP 3141** and the
"numbers" module regarding a type hierarchy for numbers based on
ABCs.)

The "collections" module has some concrete classes that derive from
ABCs; these can, of course, be further derived. In addition, the
"collections.abc" 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 "ABCMeta" for defining ABCs and a
helper class "ABC" to alternatively define ABCs through inheritance:

class abc.ABC

   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:

      from abc import ABC

      class MyABC(ABC):
          pass

   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:

      from abc import ABCMeta

      class MyABC(metaclass=ABCMeta):
          pass

   Nowe w wersji 3.4.

class abc.ABCMeta

   Pośrednie uogólnienie dla definiowania abstrakcyjnych uogólnień
   podstawowych (w skr. z ang. - ABC - Abstract Base Class).

   Używaj tego uogólnienia pośredniego aby utworzyć abstrakcyjne
   uogólnienie podstawowe (w skr. z ang. ABC). ABC może być
   wykorzystane do tworzenia następnych uogólnień bezpośrednio, i
   wtedy działa jako uogólnienie domieszki. Możesz także zarejestrować
   niezwiązane uogólnienia konkretne (nawet wbudowane uogólnienia) i
   niezwiązane abstrakcyjne uogólnienia podstawowe jako "sztuczne
   podrzędne uogólnienia" -- te uogólnienia i pochodne po nich będą
   uznawane za podrzędne uogólnienia rejestrowanego uogólnienia
   podstawowego abstrakcyjnego przez wbudowane zadanie "issubclass()",
   ale rejestrowanie abstrakcyjnego uogólnienia bazowego nie pokaże
   się w ich sposobie rozwiązywania sposobów postępowania (w skr. MRO
   - z ang. - Method Resolution Order) ani też wypełnienia sposobów
   postępowania określone przez rejestrowanie abstrakcyjnych bazowych
   uogólnień nie będą wywoływalne (nawet nie przez użycie "super()").
   [1]

   Classes created with a metaclass of "ABCMeta" have the following
   method:

   register(subclass)

      Zarejestruj *podrzędne uogólnienie* jako "wirtualne podrzędne
      uogólnienie" tego uogólnienia abstrakcyjnego podstawowego. Na
      przykład:

         from abc import ABC

         class MyABC(ABC):
             pass

         MyABC.register(tuple)

         assert issubclass(tuple, MyABC)
         assert isinstance((), MyABC)

      Zmienione w wersji 3.3: Returns the registered subclass, to
      allow usage as a class decorator.

      Zmienione w wersji 3.4: To detect calls to "register()", you can
      use the "get_cache_token()" function.

   Możesz także obejść ten sposób postępowania w abstrakcyjnym bazowym
   uogólnieniu:

   __subclasshook__(subclass)

      (Musi być określona jako sposób postępowania uogólnienia.)

      Check whether *subclass* is considered a subclass of this ABC.
      This means that you can customize the behavior of "issubclass()"
      further without the need to call "register()" on every class you
      want to consider a subclass of the ABC.  (This class method is
      called from the "__subclasscheck__()" method of the ABC.)

      This method should return "True", "False" or "NotImplemented".
      If it returns "True", the *subclass* is considered a subclass of
      this ABC. If it returns "False", the *subclass* is not
      considered a subclass of this ABC, even if it would normally be
      one.  If it returns "NotImplemented", the subclass check is
      continued with the usual mechanism.

   Dla demonstracji tych pomysłów, popatrz na tę przykładową definicję
   abstrakcyjnego uogólnienia podstawowego:

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

   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.

   Finally, the last line makes "Foo" a virtual subclass of
   "MyIterable", even though it does not define an "__iter__()" method
   (it uses the old-style iterable protocol, defined in terms of
   "__len__()" and "__getitem__()").  Note that this will not make
   "get_iterator" available as a method of "Foo", so it is provided
   separately.

The "abc" module also provides the following decorator:

@abc.abstractmethod

   Dekorator wskazujący abstrakcyjne sposoby postępowania.

   Using this decorator requires that the class's metaclass is
   "ABCMeta" or is derived from it.  A class that has a metaclass
   derived from "ABCMeta" 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.  "abstractmethod()" 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 "update_abstractmethods()"
   function.  The "abstractmethod()" only affects subclasses derived
   using regular inheritance; "virtual subclasses" registered with the
   ABC's "register()" method are not affected.

   When "abstractmethod()" 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
   "__isabstractmethod__". In general, this attribute should be "True"
   if any of the methods used to compose the descriptor are abstract.
   For example, Python's built-in "property" 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))

   Informacja:

     W przeciwieństwie do abstrakcyjnych sposobów postępowania Javy,
     te abstrakcyjne sposoby postępowania mogą mieć swoje wypełnienie.
     To wypełnienie może być wzywane przez mechanizm odwołań do
     zadania "super()", z uogólnienia które przesłania taki sposób
     postępowania. To może być użyteczne jako punkt końcowy super-
     wywołania w ramach udogodnienia które używa współpracującego
     wielokrotnego-dziedziczenia.

The "abc" module also supports the following legacy decorators:

@abc.abstractclassmethod

   Nowe w wersji 3.2.

   Niezalecane od wersji 3.3: It is now possible to use "classmethod"
   with "abstractmethod()", making this decorator redundant.

   A subclass of the built-in "classmethod()", indicating an abstract
   classmethod. Otherwise it is similar to "abstractmethod()".

   This special case is deprecated, as the "classmethod()" decorator
   is now correctly identified as abstract when applied to an abstract
   method:

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

@abc.abstractstaticmethod

   Nowe w wersji 3.2.

   Niezalecane od wersji 3.3: It is now possible to use "staticmethod"
   with "abstractmethod()", making this decorator redundant.

   A subclass of the built-in "staticmethod()", indicating an abstract
   staticmethod. Otherwise it is similar to "abstractmethod()".

   This special case is deprecated, as the "staticmethod()" decorator
   is now correctly identified as abstract when applied to an abstract
   method:

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

@abc.abstractproperty

   Niezalecane od wersji 3.3: It is now possible to use "property",
   "property.getter()", "property.setter()" and "property.deleter()"
   with "abstractmethod()", making this decorator redundant.

   Podrzędne uogólnienie wbudowanego zadania "property()" wskazujące
   abstrakcyjną właściwość.

   This special case is deprecated, as the "property()" 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:

      class D(C):
          @C.x.setter
          def x(self, val):
              ...

The "abc" module also provides the following functions:

abc.get_cache_token()

   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
   "ABCMeta.register()" on any ABC.

   Nowe w wersji 3.4.

abc.update_abstractmethods(cls)

   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 "ABCMeta", does nothing.

   Informacja:

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

   Nowe w wersji 3.10.

-[ Przypisy ]-

[1] Programiści C++ powinni zauważyć, że koncepcja wirtualnego
    uogólnienia podstawowego z języka pytonowskiego nie jest tożsame z
    tym z C++'a.
