"collections.abc" --- Abstract Base Classes for Containers
**********************************************************

Νέο στην έκδοση 3.3: Παλαιότερα, αυτό το module ήταν μέρος του
"collections" module.

**Πηγαίος κώδικας:** Lib/_collections_abc.py

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

This module provides *abstract base classes* that can be used to test
whether a class provides a particular interface; for example, whether
it is *hashable* or whether it is a mapping.

Ένας έλεγχος "issubclass()" ή "isinstance()" για μια διεπαφή
λειτουργεί με έναν από τρεις τρόπους.

1) A newly written class can inherit directly from one of the abstract
base classes.  The class must supply the required abstract methods.
The remaining mixin methods come from inheritance and can be
overridden if desired.  Other methods may be added as needed:

   class C(Sequence):                      # Direct inheritance
       def __init__(self): ...             # Extra method not required by the ABC
       def __getitem__(self, index):  ...  # Required abstract method
       def __len__(self):  ...             # Required abstract method
       def count(self, value): ...         # Optionally override a mixin method

   >>> issubclass(C, Sequence)
   True
   >>> isinstance(C(), Sequence)
   True

2) Existing classes and built-in classes can be registered as "virtual
subclasses" of the ABCs.  Those classes should define the full API
including all of the abstract methods and all of the mixin methods.
This lets users rely on "issubclass()" or "isinstance()" tests to
determine whether the full interface is supported.  The exception to
this rule is for methods that are automatically inferred from the rest
of the API:

   class D:                                 # No inheritance
       def __init__(self): ...              # Extra method not required by the ABC
       def __getitem__(self, index):  ...   # Abstract method
       def __len__(self):  ...              # Abstract method
       def count(self, value): ...          # Mixin method
       def index(self, value): ...          # Mixin method

   Sequence.register(D)                     # Register instead of inherit

   >>> issubclass(D, Sequence)
   True
   >>> isinstance(D(), Sequence)
   True

In this example, class "D" does not need to define "__contains__",
"__iter__", and "__reversed__" because the in-operator, the
*iteration* logic, and the "reversed()" function automatically fall
back to using "__getitem__" and "__len__".

3) Some simple interfaces are directly recognizable by the presence of
the required methods (unless those methods have been set to "None"):

   class E:
       def __iter__(self): ...
       def __next__(next): ...

   >>> issubclass(E, Iterable)
   True
   >>> isinstance(E(), Iterable)
   True

Οι σύνθετες διεπαφές δεν υποστηρίζουν αυτή την τελευταία τεχνική
επειδή μια διεπαφή είναι κάτι περισσότερο από την παρουσία ονομάτων
μεθόδων. Οι διεπαφές καθορίζουν τη σημασιολογία και τις σχέσεις μεταξύ
των μεθόδων που δεν μπορούν να συναχθούν αποκλειστικά από την παρουσία
συγκεκριμένων ονομάτων μεθόδων. Για παράδειγμα, η γνώση ότι μια κλάση
παρέχει τις μεθόδους "__getitem__", "__len__" και "__iter__" δεν είναι
επαρκής για να διακρίνει μια κλάση "Sequence" από μια κλάση "Mapping".

Νέο στην έκδοση 3.9: Αυτές οι αφηρημένες κλάσεις υποστηρίζουν πλέον
"[]". Δείτε Τύπος Generic Alias και **PEP 585**.


Αφηρημένες Βασικές Κλάσεις Συλλογών
===================================

Το collections module προσφέρει τις εξής *ABCs*:

+--------------------------------+------------------------+-------------------------+------------------------------------------------------+
| ABC                            | Κληρονομεί από         | Αφηρημένες Μέθοδοι      | Mixin Μέθοδοι                                        |
|================================|========================|=========================|======================================================|
| "Container" [1]                |                        | "__contains__"          |                                                      |
+--------------------------------+------------------------+-------------------------+------------------------------------------------------+
| "Hashable" [1]                 |                        | "__hash__"              |                                                      |
+--------------------------------+------------------------+-------------------------+------------------------------------------------------+
| "Iterable" [1] [2]             |                        | "__iter__"              |                                                      |
+--------------------------------+------------------------+-------------------------+------------------------------------------------------+
| "Iterator" [1]                 | "Iterable"             | "__next__"              | "__iter__"                                           |
+--------------------------------+------------------------+-------------------------+------------------------------------------------------+
| "Reversible" [1]               | "Iterable"             | "__reversed__"          |                                                      |
+--------------------------------+------------------------+-------------------------+------------------------------------------------------+
| "Generator"  [1]               | "Iterator"             | "send", "throw"         | "close", "__iter__", "__next__"                      |
+--------------------------------+------------------------+-------------------------+------------------------------------------------------+
| "Sized"  [1]                   |                        | "__len__"               |                                                      |
+--------------------------------+------------------------+-------------------------+------------------------------------------------------+
| "Callable"  [1]                |                        | "__call__"              |                                                      |
+--------------------------------+------------------------+-------------------------+------------------------------------------------------+
| "Collection"  [1]              | "Sized", "Iterable",   | "__contains__",         |                                                      |
|                                | "Container"            | "__iter__", "__len__"   |                                                      |
+--------------------------------+------------------------+-------------------------+------------------------------------------------------+
| "Sequence"                     | "Reversible",          | "__getitem__",          | "__contains__", "__iter__", "__reversed__", "index", |
|                                | "Collection"           | "__len__"               | and "count"                                          |
+--------------------------------+------------------------+-------------------------+------------------------------------------------------+
| "MutableSequence"              | "Sequence"             | "__getitem__",          | Inherited "Sequence" methods and "append",           |
|                                |                        | "__setitem__",          | "reverse", "extend", "pop", "remove", and "__iadd__" |
|                                |                        | "__delitem__",          |                                                      |
|                                |                        | "__len__", "insert"     |                                                      |
+--------------------------------+------------------------+-------------------------+------------------------------------------------------+
| "ByteString"                   | "Sequence"             | "__getitem__",          | Κληρονομημένες "Sequence" μέθοδοι                    |
|                                |                        | "__len__"               |                                                      |
+--------------------------------+------------------------+-------------------------+------------------------------------------------------+
| "Set"                          | "Collection"           | "__contains__",         | "__le__", "__lt__", "__eq__", "__ne__", "__gt__",    |
|                                |                        | "__iter__", "__len__"   | "__ge__", "__and__", "__or__", "__sub__", "__xor__", |
|                                |                        |                         | and "isdisjoint"                                     |
+--------------------------------+------------------------+-------------------------+------------------------------------------------------+
| "MutableSet"                   | "Set"                  | "__contains__",         | Κληρονομημένες "Set" μέθοδοι και "clear", "pop",     |
|                                |                        | "__iter__", "__len__",  | "remove", "__ior__", "__iand__", "__ixor__", και     |
|                                |                        | "add", "discard"        | "__isub__"                                           |
+--------------------------------+------------------------+-------------------------+------------------------------------------------------+
| "Mapping"                      | "Collection"           | "__getitem__",          | "__contains__", "keys", "items", "values", "get",    |
|                                |                        | "__iter__", "__len__"   | "__eq__", και "__ne__"                               |
+--------------------------------+------------------------+-------------------------+------------------------------------------------------+
| "MutableMapping"               | "Mapping"              | "__getitem__",          | Κληρονομημένες "Mapping" μέθοδοι και "pop",          |
|                                |                        | "__setitem__",          | "popitem", "clear", "update", και "setdefault"       |
|                                |                        | "__delitem__",          |                                                      |
|                                |                        | "__iter__", "__len__"   |                                                      |
+--------------------------------+------------------------+-------------------------+------------------------------------------------------+
| "MappingView"                  | "Sized"                |                         | "__len__"                                            |
+--------------------------------+------------------------+-------------------------+------------------------------------------------------+
| "ItemsView"                    | "MappingView", "Set"   |                         | "__contains__", "__iter__"                           |
+--------------------------------+------------------------+-------------------------+------------------------------------------------------+
| "KeysView"                     | "MappingView", "Set"   |                         | "__contains__", "__iter__"                           |
+--------------------------------+------------------------+-------------------------+------------------------------------------------------+
| "ValuesView"                   | "MappingView",         |                         | "__contains__", "__iter__"                           |
|                                | "Collection"           |                         |                                                      |
+--------------------------------+------------------------+-------------------------+------------------------------------------------------+
| "Awaitable" [1]                |                        | "__await__"             |                                                      |
+--------------------------------+------------------------+-------------------------+------------------------------------------------------+
| "Coroutine" [1]                | "Awaitable"            | "send", "throw"         | "close"                                              |
+--------------------------------+------------------------+-------------------------+------------------------------------------------------+
| "AsyncIterable" [1]            |                        | "__aiter__"             |                                                      |
+--------------------------------+------------------------+-------------------------+------------------------------------------------------+
| "AsyncIterator" [1]            | "AsyncIterable"        | "__anext__"             | "__aiter__"                                          |
+--------------------------------+------------------------+-------------------------+------------------------------------------------------+
| "AsyncGenerator" [1]           | "AsyncIterator"        | "asend", "athrow"       | "aclose", "__aiter__", "__anext__"                   |
+--------------------------------+------------------------+-------------------------+------------------------------------------------------+

-[ Υποσημειώσεις ]-

[1] These ABCs override "object.__subclasshook__()" to support testing
    an interface by verifying the required methods are present and
    have not been set to "None".  This only works for simple
    interfaces.  More complex interfaces require registration or
    direct subclassing.

[2] Checking "isinstance(obj, Iterable)" detects classes that are
    registered as "Iterable" or that have an "__iter__()" method, but
    it does not detect classes that iterate with the "__getitem__()"
    method.  The only reliable way to determine whether an object is
    *iterable* is to call "iter(obj)".


Αφηρημένες Βασικές Κλάσεις Συλλογών -- Αναλυτικές Περιγραφές
============================================================

class collections.abc.Container

   ABC for classes that provide the "__contains__()" method.

class collections.abc.Hashable

   ABC for classes that provide the "__hash__()" method.

class collections.abc.Sized

   ABC for classes that provide the "__len__()" method.

class collections.abc.Callable

   ABC for classes that provide the "__call__()" method.

class collections.abc.Iterable

   ABC for classes that provide the "__iter__()" method.

   Checking "isinstance(obj, Iterable)" detects classes that are
   registered as "Iterable" or that have an "__iter__()" method, but
   it does not detect classes that iterate with the "__getitem__()"
   method. The only reliable way to determine whether an object is
   *iterable* is to call "iter(obj)".

class collections.abc.Collection

   ABC για τις κλάσεις επαναλαμβανόμενων container με μέγεθος.

   Νέο στην έκδοση 3.6.

class collections.abc.Iterator

   ABC για κλάσεις που παρέχουν τις μεθόδους "__iter__()" και
   "__next__()". Δείτε επίσης τον ορισμό του *iterator*.

class collections.abc.Reversible

   ABC for iterable classes that also provide the "__reversed__()"
   method.

   Νέο στην έκδοση 3.6.

class collections.abc.Generator

   ABC for generator classes that implement the protocol defined in
   **PEP 342** that extends iterators with the "send()", "throw()" and
   "close()" methods. See also the definition of *generator*.

   Νέο στην έκδοση 3.5.

class collections.abc.Sequence
class collections.abc.MutableSequence
class collections.abc.ByteString

   ABCs μόνο για ανάγνωση (read-only) και mutable *sequences*.

   Implementation note: Some of the mixin methods, such as
   "__iter__()", "__reversed__()" and "index()", make repeated calls
   to the underlying "__getitem__()" method. Consequently, if
   "__getitem__()" is implemented with constant access speed, the
   mixin methods will have linear performance; however, if the
   underlying method is linear (as it would be with a linked list),
   the mixins will have quadratic performance and will likely need to
   be overridden.

   Άλλαξε στην έκδοση 3.5: Η μέθοδος index() πρόσθεσε υποστήριξη για
   τα ορίσματα *stop* και *start*.

class collections.abc.Set
class collections.abc.MutableSet

   ABCs for read-only and mutable sets.

class collections.abc.Mapping
class collections.abc.MutableMapping

   ABCs μόνο για ανάγνωση (read-only) και mutable *mappings*.

class collections.abc.MappingView
class collections.abc.ItemsView
class collections.abc.KeysView
class collections.abc.ValuesView

   ABCs για αντιστοιχήσεις, στοιχεία, κλειδιά και τιμές *views*.

class collections.abc.Awaitable

   ABC for *awaitable* objects, which can be used in "await"
   expressions.  Custom implementations must provide the "__await__()"
   method.

   Τα αντικείμενα *Coroutine* και τα στιγμιότυπα της κλάσης
   "Coroutine" είναι όλα παραδείγματα αυτής της ABC.

   Σημείωση:

     In CPython, generator-based coroutines (generators decorated with
     "types.coroutine()" or "asyncio.coroutine()") are *awaitables*,
     even though they do not have an "__await__()" method. Using
     "isinstance(gencoro, Awaitable)" for them will return "False".
     Use "inspect.isawaitable()" to detect them.

   Νέο στην έκδοση 3.5.

class collections.abc.Coroutine

   ABC for coroutine compatible classes.  These implement the
   following methods, defined in Coroutine Objects: "send()",
   "throw()", and "close()".  Custom implementations must also
   implement "__await__()".  All "Coroutine" instances are also
   instances of "Awaitable".  See also the definition of *coroutine*.

   Σημείωση:

     In CPython, generator-based coroutines (generators decorated with
     "types.coroutine()" or "asyncio.coroutine()") are *awaitables*,
     even though they do not have an "__await__()" method. Using
     "isinstance(gencoro, Coroutine)" for them will return "False".
     Use "inspect.isawaitable()" to detect them.

   Νέο στην έκδοση 3.5.

class collections.abc.AsyncIterable

   ABC for classes that provide "__aiter__" method.  See also the
   definition of *asynchronous iterable*.

   Νέο στην έκδοση 3.5.

class collections.abc.AsyncIterator

   ABC για κλάσεις που παρέχουν τις μεθόδους "__aiter__" και
   "__anext__". Δείτε επίσης τον ορισμό του *asynchronous iterator*.

   Νέο στην έκδοση 3.5.

class collections.abc.AsyncGenerator

   ABC for asynchronous generator classes that implement the protocol
   defined in **PEP 525** and **PEP 492**.

   Νέο στην έκδοση 3.6.


Παραδείγματα και Συνταγές
=========================

Οι ABCs επιτρέπουν να ρωτήσουμε τις κλάσεις ή τα αντικείμενα αν
παρέχουν συγκεκριμένη λειτουργικότητα, για παράδειγμα:

   size = None
   if isinstance(myvar, collections.abc.Sized):
       size = len(myvar)

Several of the ABCs are also useful as mixins that make it easier to
develop classes supporting container APIs.  For example, to write a
class supporting the full "Set" API, it is only necessary to supply
the three underlying abstract methods: "__contains__()", "__iter__()",
and "__len__()". The ABC supplies the remaining methods such as
"__and__()" and "isdisjoint()":

   class ListBasedSet(collections.abc.Set):
       ''' Alternate set implementation favoring space over speed
           and not requiring the set elements to be hashable. '''
       def __init__(self, iterable):
           self.elements = lst = []
           for value in iterable:
               if value not in lst:
                   lst.append(value)

       def __iter__(self):
           return iter(self.elements)

       def __contains__(self, value):
           return value in self.elements

       def __len__(self):
           return len(self.elements)

   s1 = ListBasedSet('abcdef')
   s2 = ListBasedSet('defghi')
   overlap = s1 & s2            # The __and__() method is supported automatically

Σημειώσεις για τη χρήση των "Set" και "MutableSet" ως mixin:

1. Since some set operations create new sets, the default mixin
   methods need a way to create new instances from an iterable. The
   class constructor is assumed to have a signature in the form
   "ClassName(iterable)". That assumption is factored-out to an
   internal classmethod called "_from_iterable()" which calls
   "cls(iterable)" to produce a new set. If the "Set" mixin is being
   used in a class with a different constructor signature, you will
   need to override "_from_iterable()" with a classmethod or regular
   method that can construct new instances from an iterable argument.

2. To override the comparisons (presumably for speed, as the semantics
   are fixed), redefine "__le__()" and "__ge__()", then the other
   operations will automatically follow suit.

3. The "Set" mixin provides a "_hash()" method to compute a hash value
   for the set; however, "__hash__()" is not defined because not all
   sets are *hashable* or immutable.  To add set hashability using
   mixins, inherit from both "Set()" and "Hashable()", then define
   "__hash__ = Set._hash".

Δείτε επίσης:

  * Συνταγή OrderedSet για ένα παράδειγμα που βασίζεται στην κλάση
    "MutableSet".

  * Για περισσότερα σχετικά με τις ABCs, δείτε το "abc" module και το
    **PEP 3119**.
