Lib/_abcoll.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.

DON'T USE THIS MODULE DIRECTLY!  The classes here should be imported
via collections; they are defined here only to alleviate certain
bootstrapping issues.  Unit tests are in test_collections.
"""

from abc import ABCMeta, abstractmethod

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

### ONE-TRICK PONIES ###

class Hashable(metaclass=ABCMeta):

    @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):

    @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(metaclass=ABCMeta):

    @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__):
                return True
        return NotImplemented


class Sized(metaclass=ABCMeta):

    @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):

    @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):

    @abstractmethod
    def __contains__(self, x):
        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(metaclass=ABCMeta):

    """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.
    """

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

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

    @abstractmethod
    def __len__(self):
        return 0

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

    @classmethod
    def _from_iterable(cls, it):
        return frozenset(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 __or__(self, other):
        if not isinstance(other, Iterable):
            return NotImplemented
        return self._from_iterable(itertools.chain(self, other))

    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.maxint
        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):

    @abstractmethod
    def add(self, value):
        """Return True if it was added, False if already there."""
        raise NotImplementedError

    @abstractmethod
    def discard(self, value):
        """Return True if it was deleted, False if not there."""
        raise NotImplementedError

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

    def toggle(self, value):
        """Return True if it was added, False if deleted."""
        # XXX This implementation is not thread-safe
        if value in self:
            self.discard(value)
            return False
        else:
            self.add(value)
            return True

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

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

    def __iand__(self, c: Container):
        for value in self:
            if value not in c:
                self.discard(value)
        return self

    def __ixor__(self, it: Iterable):
        # This calls toggle(), so if that is overridded, we call the override
        for value in it:
            self.toggle(it)
        return self

    def __isub__(self, it: Iterable):
        for value in it:
            self.discard(value)
        return self

MutableSet.register(set)


### MAPPINGS ###


class Mapping(metaclass=ABCMeta):

    @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

    @abstractmethod
    def __len__(self):
        return 0

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

    def keys(self):
        return KeysView(self)

    def items(self):
        return ItemsView(self)

    def values(self):
        return ValuesView(self)


class MappingView(metaclass=ABCMeta):

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

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


class KeysView(MappingView, Set):

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

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

KeysView.register(type({}.keys()))


class ItemsView(MappingView, Set):

    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(type({}.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(type({}.values()))


class MutableMapping(Mapping):

    @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(self, other=(), **kwds):
        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

MutableMapping.register(dict)


### SEQUENCES ###


class Sequence(metaclass=ABCMeta):

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

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

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

    @abstractmethod
    def __len__(self):
        return 0

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

    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(bytes)
Sequence.register(memoryview)


class MutableSequence(Sequence):

    @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 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)

MutableSequence.register(list)
MutableSequence.register(bytes)