abc.py

# Copyright 2007 Google, Inc. All Rights Reserved.
# Licensed to PSF under a Contributor Agreement.

"""Abstract Base Classes (ABCs) for collections, according to PEP 3119.

Unit tests are in test_collections.
"""

from abc import ABCMeta, abstractmethod
import sys

__all__ = ["Hashable", "Iterable", "Iterator",
           "Sized", "Container", "Callable",
           "Set", "MutableSet",
           "Mapping", "MutableMapping",
           "MappingView", "KeysView", "ItemsView", "ValuesView",
           "Sequence", "MutableSequence",
           "ByteString",
           ]

# Private list of types that we want to register with the various ABCs
# so that they will pass tests like:
#       it = iter(somebytearray)
#       assert isinstance(it, Iterable)
# Note:  in other implementations, these types many not be distinct
# and they make have their own implementation specific types that
# are not included on this list.
bytes_iterator = type(iter(b''))
bytearray_iterator = type(iter(bytearray()))
#callable_iterator = ???
dict_keyiterator = type(iter({}.keys()))
dict_valueiterator = type(iter({}.values()))
dict_itemiterator = type(iter({}.items()))
list_iterator = type(iter([]))
list_reverseiterator = type(iter(reversed([])))
range_iterator = type(iter(range(0)))
set_iterator = type(iter(set()))
str_iterator = type(iter(""))
tuple_iterator = type(iter(()))
zip_iterator = type(iter(zip()))
## views ##
dict_keys = type({}.keys())
dict_values = type({}.values())
dict_items = type({}.items())
## misc ##
mappingproxy = type(type.__dict__)


### ONE-TRICK PONIES ###

class Hashable(metaclass=ABCMeta):

    __slots__ = ()

    @abstractmethod
    def __hash__(self):
        return 0

    @classmethod
    def __subclasshook__(cls, C):
        if cls is Hashable:
            for B in C.__mro__:
                if "__hash__" in B.__dict__:
                    if B.__dict__["__hash__"]:
                        return True
                    break
        return NotImplemented


class Iterable(metaclass=ABCMeta):

    __slots__ = ()

    @abstractmethod
    def __iter__(self):
        while False:
            yield None

    @classmethod
    def __subclasshook__(cls, C):
        if cls is Iterable:
            if any("__iter__" in B.__dict__ for B in C.__mro__):
                return True
        return NotImplemented


class Iterator(Iterable):

    __slots__ = ()

    @abstractmethod
    def __next__(self):
        raise StopIteration

    def __iter__(self):
        return self

    @classmethod
    def __subclasshook__(cls, C):
        if cls is Iterator:
            if (any("__next__" in B.__dict__ for B in C.__mro__) and
                any("__iter__" in B.__dict__ for B in C.__mro__)):
                return True
        return NotImplemented

Iterator.register(bytes_iterator)
Iterator.register(bytearray_iterator)
#Iterator.register(callable_iterator)
Iterator.register(dict_keyiterator)
Iterator.register(dict_valueiterator)
Iterator.register(dict_itemiterator)
Iterator.register(list_iterator)
Iterator.register(list_reverseiterator)
Iterator.register(range_iterator)
Iterator.register(set_iterator)
Iterator.register(str_iterator)
Iterator.register(tuple_iterator)
Iterator.register(zip_iterator)

class Sized(metaclass=ABCMeta):

    __slots__ = ()

    @abstractmethod
    def __len__(self):
        return 0

    @classmethod
    def __subclasshook__(cls, C):
        if cls is Sized:
            if any("__len__" in B.__dict__ for B in C.__mro__):
                return True
        return NotImplemented


class Container(metaclass=ABCMeta):

    __slots__ = ()

    @abstractmethod
    def __contains__(self, x):
        return False

    @classmethod
    def __subclasshook__(cls, C):
        if cls is Container:
            if any("__contains__" in B.__dict__ for B in C.__mro__):
                return True
        return NotImplemented


class Callable(metaclass=ABCMeta):

    __slots__ = ()

    @abstractmethod
    def __call__(self, *args, **kwds):
        return False

    @classmethod
    def __subclasshook__(cls, C):
        if cls is Callable:
            if any("__call__" in B.__dict__ for B in C.__mro__):
                return True
        return NotImplemented


### SETS ###


class Set(Sized, Iterable, Container):

    """A set is a finite, iterable container.

    This class provides concrete generic implementations of all
    methods except for __contains__, __iter__ and __len__.

    To override the comparisons (presumably for speed, as the
    semantics are fixed), all you have to do is redefine __le__ and
    then the other operations will automatically follow suit.
    """

    __slots__ = ()

    def __le__(self, other):
        if not isinstance(other, Set):
            return NotImplemented
        if len(self) > len(other):
            return False
        for elem in self:
            if elem not in other:
                return False
        return True

    def __lt__(self, other):
        if not isinstance(other, Set):
            return NotImplemented
        return len(self) < len(other) and self.__le__(other)

    def __gt__(self, other):
        if not isinstance(other, Set):
            return NotImplemented
        return other.__lt__(self)

    def __ge__(self, other):
        if not isinstance(other, Set):
            return NotImplemented
        return other.__le__(self)

    def __eq__(self, other):
        if not isinstance(other, Set):
            return NotImplemented
        return len(self) == len(other) and self.__le__(other)

    def __ne__(self, other):
        return not (self == other)

    @classmethod
    def _from_iterable(cls, it):
        '''Construct an instance of the class from any iterable input.

        Must override this method if the class constructor signature
        does not accept an iterable for an input.
        '''
        return cls(it)

    def __and__(self, other):
        if not isinstance(other, Iterable):
            return NotImplemented
        return self._from_iterable(value for value in other if value in self)

    def isdisjoint(self, other):
        for value in other:
            if value in self:
                return False
        return True

    def __or__(self, other):
        if not isinstance(other, Iterable):
            return NotImplemented
        chain = (e for s in (self, other) for e in s)
        return self._from_iterable(chain)

    def __sub__(self, other):
        if not isinstance(other, Set):
            if not isinstance(other, Iterable):
                return NotImplemented
            other = self._from_iterable(other)
        return self._from_iterable(value for value in self
                                   if value not in other)

    def __xor__(self, other):
        if not isinstance(other, Set):
            if not isinstance(other, Iterable):
                return NotImplemented
            other = self._from_iterable(other)
        return (self - other) | (other - self)

    def _hash(self):
        """Compute the hash value of a set.

        Note that we don't define __hash__: not all sets are hashable.
        But if you define a hashable set type, its __hash__ should
        call this function.

        This must be compatible __eq__.

        All sets ought to compare equal if they contain the same
        elements, regardless of how they are implemented, and
        regardless of the order of the elements; so there's not much
        freedom for __eq__ or __hash__.  We match the algorithm used
        by the built-in frozenset type.
        """
        MAX = sys.maxsize
        MASK = 2 * MAX + 1
        n = len(self)
        h = 1927868237 * (n + 1)
        h &= MASK
        for x in self:
            hx = hash(x)
            h ^= (hx ^ (hx << 16) ^ 89869747)  * 3644798167
            h &= MASK
        h = h * 69069 + 907133923
        h &= MASK
        if h > MAX:
            h -= MASK + 1
        if h == -1:
            h = 590923713
        return h

Set.register(frozenset)


class MutableSet(Set):

    __slots__ = ()

    @abstractmethod
    def add(self, value):
        """Add an element."""
        raise NotImplementedError

    @abstractmethod
    def discard(self, value):
        """Remove an element.  Do not raise an exception if absent."""
        raise NotImplementedError

    def remove(self, value):
        """Remove an element. If not a member, raise a KeyError."""
        if value not in self:
            raise KeyError(value)
        self.discard(value)

    def pop(self):
        """Return the popped value.  Raise KeyError if empty."""
        it = iter(self)
        try:
            value = next(it)
        except StopIteration:
            raise KeyError
        self.discard(value)
        return value

    def clear(self):
        """This is slow (creates N new iterators!) but effective."""
        try:
            while True:
                self.pop()
        except KeyError:
            pass

    def __ior__(self, it):
        for value in it:
            self.add(value)
        return self

    def __iand__(self, it):
        for value in (self - it):
            self.discard(value)
        return self

    def __ixor__(self, it):
        if it is self:
            self.clear()
        else:
            if not isinstance(it, Set):
                it = self._from_iterable(it)
            for value in it:
                if value in self:
                    self.discard(value)
                else:
                    self.add(value)
        return self

    def __isub__(self, it):
        if it is self:
            self.clear()
        else:
            for value in it:
                self.discard(value)
        return self

MutableSet.register(set)


### MAPPINGS ###


class Mapping(Sized, Iterable, Container):

    __slots__ = ()

    @abstractmethod
    def __getitem__(self, key):
        raise KeyError

    def get(self, key, default=None):
        try:
            return self[key]
        except KeyError:
            return default

    def __contains__(self, key):
        try:
            self[key]
        except KeyError:
            return False
        else:
            return True

    def keys(self):
        return KeysView(self)

    def items(self):
        return ItemsView(self)

    def values(self):
        return ValuesView(self)

    def __eq__(self, other):
        if not isinstance(other, Mapping):
            return NotImplemented
        return dict(self.items()) == dict(other.items())

    def __ne__(self, other):
        return not (self == other)

Mapping.register(mappingproxy)


class MappingView(Sized):

    def __init__(self, mapping):
        self._mapping = mapping

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

    def __repr__(self):
        return '{0.__class__.__name__}({0._mapping!r})'.format(self)


class KeysView(MappingView, Set):

    @classmethod
    def _from_iterable(self, it):
        return set(it)

    def __contains__(self, key):
        return key in self._mapping

    def __iter__(self):
        yield from self._mapping

KeysView.register(dict_keys)


class ItemsView(MappingView, Set):

    @classmethod
    def _from_iterable(self, it):
        return set(it)

    def __contains__(self, item):
        key, value = item
        try:
            v = self._mapping[key]
        except KeyError:
            return False
        else:
            return v == value

    def __iter__(self):
        for key in self._mapping:
            yield (key, self._mapping[key])

ItemsView.register(dict_items)


class ValuesView(MappingView):

    def __contains__(self, value):
        for key in self._mapping:
            if value == self._mapping[key]:
                return True
        return False

    def __iter__(self):
        for key in self._mapping:
            yield self._mapping[key]

ValuesView.register(dict_values)


class MutableMapping(Mapping):

    __slots__ = ()

    @abstractmethod
    def __setitem__(self, key, value):
        raise KeyError

    @abstractmethod
    def __delitem__(self, key):
        raise KeyError

    __marker = object()

    def pop(self, key, default=__marker):
        try:
            value = self[key]
        except KeyError:
            if default is self.__marker:
                raise
            return default
        else:
            del self[key]
            return value

    def popitem(self):
        try:
            key = next(iter(self))
        except StopIteration:
            raise KeyError
        value = self[key]
        del self[key]
        return key, value

    def clear(self):
        try:
            while True:
                self.popitem()
        except KeyError:
            pass

    def update(*args, **kwds):
        if len(args) > 2:
            raise TypeError("update() takes at most 2 positional "
                            "arguments ({} given)".format(len(args)))
        elif not args:
            raise TypeError("update() takes at least 1 argument (0 given)")
        self = args[0]
        other = args[1] if len(args) >= 2 else ()

        if isinstance(other, Mapping):
            for key in other:
                self[key] = other[key]
        elif hasattr(other, "keys"):
            for key in other.keys():
                self[key] = other[key]
        else:
            for key, value in other:
                self[key] = value
        for key, value in kwds.items():
            self[key] = value

    def setdefault(self, key, default=None):
        try:
            return self[key]
        except KeyError:
            self[key] = default
        return default

MutableMapping.register(dict)


### SEQUENCES ###


class Sequence(Sized, Iterable, Container):

    """All the operations on a read-only sequence.

    Concrete subclasses must override __new__ or __init__,
    __getitem__, and __len__.
    """

    __slots__ = ()

    @abstractmethod
    def __getitem__(self, index):
        raise IndexError

    def __iter__(self):
        i = 0
        try:
            while True:
                v = self[i]
                yield v
                i += 1
        except IndexError:
            return

    def __contains__(self, value):
        for v in self:
            if v == value:
                return True
        return False

    def __reversed__(self):
        for i in reversed(range(len(self))):
            yield self[i]

    def index(self, value):
        for i, v in enumerate(self):
            if v == value:
                return i
        raise ValueError

    def count(self, value):
        return sum(1 for v in self if v == value)

Sequence.register(tuple)
Sequence.register(str)
Sequence.register(range)


class ByteString(Sequence):

    """This unifies bytes and bytearray.

    XXX Should add all their methods.
    """

    __slots__ = ()

ByteString.register(bytes)
ByteString.register(bytearray)


class MutableSequence(Sequence):

    __slots__ = ()

    @abstractmethod
    def __setitem__(self, index, value):
        raise IndexError

    @abstractmethod
    def __delitem__(self, index):
        raise IndexError

    @abstractmethod
    def insert(self, index, value):
        raise IndexError

    def append(self, value):
        self.insert(len(self), value)

    def clear(self):
        try:
            while True:
                self.pop()
        except IndexError:
            pass

    def reverse(self):
        n = len(self)
        for i in range(n//2):
            self[i], self[n-i-1] = self[n-i-1], self[i]

    def extend(self, values):
        for v in values:
            self.append(v)

    def pop(self, index=-1):
        v = self[index]
        del self[index]
        return v

    def remove(self, value):
        del self[self.index(value)]

    def __iadd__(self, values):
        self.extend(values)
        return self

MutableSequence.register(list)
MutableSequence.register(bytearray)  # Multiply inheriting, see ByteString