"""
Sets

AUTHORS:

- William Stein (2005) - first version

- William Stein (2006-02-16) - large number of documentation and
  examples; improved code

- Mike Hansen (2007-3-25) - added differences and symmetric
  differences; fixed operators

- Florent Hivert (2010-06-17) - Adapted to categories

- Nicolas M. Thiery (2011-03-15) - Added subset and superset methods

- Julian Rueth (2013-04-09) - Collected common code in
  :class:`Set_object_binary`, fixed ``__hash__``.

"""

#*****************************************************************************
#       Copyright (C) 2005 William Stein <wstein@gmail.com>
#                     2013 Julian Rueth <julian.rueth@fsfe.org>
#
#  Distributed under the terms of the GNU General Public License (GPL)
#
#    This code is distributed in the hope that it will be useful,
#    but WITHOUT ANY WARRANTY; without even the implied warranty of
#    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
#    General Public License for more details.
#
#  The full text of the GPL is available at:
#
#                  http://www.gnu.org/licenses/
#*****************************************************************************

from sage.structure.element import Element
from sage.structure.parent import Parent, Set_generic
from sage.misc.latex import latex
import sage.rings.infinity
from sage.misc.misc import is_iterator
from sage.categories.sets_cat import Sets
from sage.categories.enumerated_sets import EnumeratedSets

def Set(X=frozenset()):
    r"""
    Create the underlying set of ``X``.

    If ``X`` is a list, tuple, Python set, or ``X.is_finite()`` is
    ``True``, this returns a wrapper around Python's enumerated immutable
    ``frozenset`` type with extra functionality.  Otherwise it returns a
    more formal wrapper.

    If you need the functionality of mutable sets, use Python's
    builtin set type.

    EXAMPLES::

        sage: X = Set(GF(9,'a'))
        sage: X
        {0, 1, 2, a, a + 1, a + 2, 2*a, 2*a + 1, 2*a + 2}
        sage: type(X)
        <class 'sage.sets.set.Set_object_enumerated_with_category'>
        sage: Y = X.union(Set(QQ))
        sage: Y
        Set-theoretic union of {0, 1, 2, a, a + 1, a + 2, 2*a, 2*a + 1, 2*a + 2} and Set of elements of Rational Field
        sage: type(Y)
        <class 'sage.sets.set.Set_object_union_with_category'>

    Usually sets can be used as dictionary keys.

    ::

        sage: d={Set([2*I,1+I]):10}
        sage: d                  # key is randomly ordered
        {{I + 1, 2*I}: 10}
        sage: d[Set([1+I,2*I])]
        10
        sage: d[Set((1+I,2*I))]
        10

    The original object is often forgotten.

    ::

        sage: v = [1,2,3]
        sage: X = Set(v)
        sage: X
        {1, 2, 3}
        sage: v.append(5)
        sage: X
        {1, 2, 3}
        sage: 5 in X
        False

    Set also accepts iterators, but be careful to only give *finite* sets.

    ::

        sage: list(Set(iter([1, 2, 3, 4, 5])))
        [1, 2, 3, 4, 5]

    We can also create sets from different types::

        sage: sorted(Set([Sequence([3,1], immutable=True), 5, QQ, Partition([3,1,1])]), key=str)
        [5, Rational Field, [3, 1, 1], [3, 1]]

    However each of the objects must be hashable::

        sage: Set([QQ, [3, 1], 5])
        Traceback (most recent call last):
        ...
        TypeError: unhashable type: 'list'

    TESTS::

        sage: Set(Primes())
        Set of all prime numbers: 2, 3, 5, 7, ...
        sage: Set(Subsets([1,2,3])).cardinality()
        8
        sage: S = Set(iter([1,2,3])); S
        {1, 2, 3}
        sage: type(S)
        <class 'sage.sets.set.Set_object_enumerated_with_category'>
        sage: S = Set([])
        sage: TestSuite(S).run()

    Check that :trac:`16090` is fixed::

        sage: Set()
        {}
    """
    if is_Set(X):
        return X

    if isinstance(X, Element):
        raise TypeError("Element has no defined underlying set")
    elif isinstance(X, (list, tuple, set, frozenset)):
        return Set_object_enumerated(frozenset(X))
    try:
        if X.is_finite():
            return Set_object_enumerated(X)
    except AttributeError:
        pass
    if is_iterator(X):
        # Note we are risking an infinite loop here,
        # but this is the way Python behaves too: try
        # sage: set(an iterator which does not terminate)
        return Set_object_enumerated(list(X))
    return Set_object(X)

def is_Set(x):
    """
    Returns ``True`` if ``x`` is a Sage :class:`Set_object` (not to be confused
    with a Python set).

    EXAMPLES::

        sage: from sage.sets.set import is_Set
        sage: is_Set([1,2,3])
        False
        sage: is_Set(set([1,2,3]))
        False
        sage: is_Set(Set([1,2,3]))
        True
        sage: is_Set(Set(QQ))
        True
        sage: is_Set(Primes())
        True
    """
    return isinstance(x, Set_generic)

class Set_object(Set_generic):
    r"""
    A set attached to an almost arbitrary object.

    EXAMPLES::

        sage: K = GF(19)
        sage: Set(K)
        {0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18}
        sage: S = Set(K)

        sage: latex(S)
        \left\{0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18\right\}
        sage: TestSuite(S).run()

        sage: latex(Set(ZZ))
        \Bold{Z}

    TESTS:

    See trac ticket :trac:`14486`::

        sage: 0 == Set([1]), Set([1]) == 0
        (False, False)
        sage: 1 == Set([0]), Set([0]) == 1
        (False, False)
    """
    def __init__(self, X):
        """
        Create a Set_object

        This function is called by the Set function; users
        shouldn't call this directly.

        EXAMPLES::

            sage: type(Set(QQ))
            <class 'sage.sets.set.Set_object_with_category'>

        TESTS::

            sage: _a, _b = get_coercion_model().canonical_coercion(Set([0]), 0)
            Traceback (most recent call last):
            ...
            TypeError: no common canonical parent for objects with parents:
            '<class 'sage.sets.set.Set_object_enumerated_with_category'>'
            and 'Integer Ring'
        """
        from sage.rings.integer import is_Integer
        if isinstance(X, (int,long)) or is_Integer(X):
            # The coercion model will try to call Set_object(0)
            raise ValueError('underlying object cannot be an integer')
        Parent.__init__(self, category=Sets())
        self.__object = X

    def __hash__(self):
        """
        Return the hash value of ``self``.

        EXAMPLES::

            sage: hash(Set(QQ)) == hash(QQ)
            True
        """
        return hash(self.__object)

    def _latex_(self):
        r"""
        Return latex representation of this set.

        This is often the same as the latex representation of this
        object when the object is infinite.

        EXAMPLES::

            sage: latex(Set(QQ))
            \Bold{Q}

        When the object is finite or a special set then the latex
        representation can be more interesting.

        ::

            sage: print latex(Primes())
            \text{\texttt{Set{ }of{ }all{ }prime{ }numbers:{ }2,{ }3,{ }5,{ }7,{ }...}}
            sage: print latex(Set([1,1,1,5,6]))
            \left\{1, 5, 6\right\}
        """
        return latex(self.__object)

    def _repr_(self):
        """
        Print representation of this set.

        EXAMPLES::

            sage: X = Set(ZZ)
            sage: X
            Set of elements of Integer Ring
            sage: X.rename('{ integers }')
            sage: X
            { integers }
        """
        return "Set of elements of %s"%self.__object

    def __iter__(self):
        """
        Iterate over the elements of this set.

        EXAMPLES::

            sage: X = Set(ZZ)
            sage: I = X.__iter__()
            sage: next(I)
            0
            sage: next(I)
            1
            sage: next(I)
            -1
            sage: next(I)
            2
        """
        return self.__object.__iter__()

    an_element = EnumeratedSets.ParentMethods.__dict__['_an_element_from_iterator']

    def __contains__(self, x):
        """
        Return ``True`` if `x` is in ``self``.

        EXAMPLES::

            sage: X = Set(ZZ)
            sage: 5 in X
            True
            sage: GF(7)(3) in X
            True
            sage: 2/1 in X
            True
            sage: 2/1 in ZZ
            True
            sage: 2/3 in X
            False

        Finite fields better illustrate the difference between
        ``__contains__`` for objects and their underlying sets.

            sage: X = Set(GF(7))
            sage: X
            {0, 1, 2, 3, 4, 5, 6}
            sage: 5/3 in X
            False
            sage: 5/3 in GF(7)
            False
            sage: Set(GF(7)).union(Set(GF(5)))
            {0, 1, 2, 3, 4, 5, 6, 1, 2, 3, 4, 0}
            sage: Set(GF(7)).intersection(Set(GF(5)))
            {}
        """
        return x in self.__object

    def __cmp__(self, right):
        r"""
        Compare ``self`` and ``right``.

        If right is not a :class:`Set_object` compare types.  If ``right`` is
        also a :class:`Set_object`, returns comparison on the underlying
        objects.

        .. NOTE::

           If `X < Y` is true this does *not* necessarily mean
           that `X` is a subset of `Y`.  Also, any two sets can be
           compared still, but the result need not be meaningful
           if they are not equal.

        EXAMPLES::

            sage: Set(ZZ) == Set(QQ)
            False
            sage: Set(ZZ) < Set(QQ)
            True
            sage: Primes() == Set(QQ)
            False

        The following is random, illustrating that comparison of
        sets is not the subset relation, when they are not equal::

            sage: Primes() < Set(QQ)             # random
            True or False
        """
        if not isinstance(right, Set_object):
            return cmp(type(self), type(right))
        return cmp(self.__object, right.__object)

    def union(self, X):
        """
        Return the union of ``self`` and ``X``.

        EXAMPLES::

            sage: Set(QQ).union(Set(ZZ))
            Set-theoretic union of Set of elements of Rational Field and Set of elements of Integer Ring
            sage: Set(QQ) + Set(ZZ)
            Set-theoretic union of Set of elements of Rational Field and Set of elements of Integer Ring
            sage: X = Set(QQ).union(Set(GF(3))); X
            Set-theoretic union of Set of elements of Rational Field and {0, 1, 2}
            sage: 2/3 in X
            True
            sage: GF(3)(2) in X
            True
            sage: GF(5)(2) in X
            False
            sage: Set(GF(7)) + Set(GF(3))
            {0, 1, 2, 3, 4, 5, 6, 1, 2, 0}
        """
        if is_Set(X):
            if self is X:
                return self
            return Set_object_union(self, X)
        raise TypeError("X (=%s) must be a Set"%X)

    def __add__(self, X):
        """
        Return the union of ``self`` and ``X``.

        EXAMPLES::

            sage: Set(RealField()) + Set(QQ^5)
             Set-theoretic union of Set of elements of Real Field with 53 bits of precision and Set of elements of Vector space of dimension 5 over Rational Field
            sage: Set(GF(3)) + Set(GF(2))
            {0, 1, 2, 0, 1}
            sage: Set(GF(2)) + Set(GF(4,'a'))
            {0, 1, a, a + 1}
            sage: Set(GF(8,'b')) + Set(GF(4,'a'))
            {0, 1, b, b + 1, b^2, b^2 + 1, b^2 + b, b^2 + b + 1, a, a + 1, 1, 0}
        """
        return self.union(X)

    def __or__(self, X):
        """
        Return the union of ``self`` and ``X``.

        EXAMPLES::

            sage: Set([2,3]) | Set([3,4])
            {2, 3, 4}
            sage: Set(ZZ) | Set(QQ)
            Set-theoretic union of Set of elements of Integer Ring and Set of elements of Rational Field
        """

        return self.union(X)

    def intersection(self, X):
        r"""
        Return the intersection of ``self`` and ``X``.

        EXAMPLES::

            sage: X = Set(ZZ).intersection(Primes())
            sage: 4 in X
            False
            sage: 3 in X
            True

            sage: 2/1 in X
            True

            sage: X = Set(GF(9,'b')).intersection(Set(GF(27,'c')))
            sage: X
            {}

            sage: X = Set(GF(9,'b')).intersection(Set(GF(27,'b')))
            sage: X
            {}
        """
        if is_Set(X):
            if self is X:
                return self
            return Set_object_intersection(self, X)
        raise TypeError("X (=%s) must be a Set"%X)


    def difference(self, X):
        r"""
        Return the set difference ``self - X``.

        EXAMPLES::

            sage: X = Set(ZZ).difference(Primes())
            sage: 4 in X
            True
            sage: 3 in X
            False

            sage: 4/1 in X
            True

            sage: X = Set(GF(9,'b')).difference(Set(GF(27,'c')))
            sage: X
            {0, 1, 2, b, b + 1, b + 2, 2*b, 2*b + 1, 2*b + 2}

            sage: X = Set(GF(9,'b')).difference(Set(GF(27,'b')))
            sage: X
            {0, 1, 2, b, b + 1, b + 2, 2*b, 2*b + 1, 2*b + 2}
        """
        if is_Set(X):
            if self is X:
                return Set([])
            return Set_object_difference(self, X)
        raise TypeError("X (=%s) must be a Set"%X)

    def symmetric_difference(self, X):
        r"""
        Returns the symmetric difference of ``self`` and ``X``.

        EXAMPLES::

            sage: X = Set([1,2,3]).symmetric_difference(Set([3,4]))
            sage: X
            {1, 2, 4}
        """

        if is_Set(X):
            if self is X:
                return Set([])
            return Set_object_symmetric_difference(self, X)
        raise TypeError("X (=%s) must be a Set"%X)


    def __sub__(self, X):
        """
        Return the difference of ``self`` and ``X``.

        EXAMPLES::

            sage: X = Set(ZZ).difference(Primes())
            sage: Y = Set(ZZ) - Primes()
            sage: X == Y
            True
        """
        return self.difference(X)

    def __and__(self, X):
        """
        Returns the intersection of ``self`` and ``X``.

        EXAMPLES::

            sage: Set([2,3]) & Set([3,4])
            {3}
            sage: Set(ZZ) & Set(QQ)
            Set-theoretic intersection of Set of elements of Integer Ring and Set of elements of Rational Field
        """

        return self.intersection(X)

    def __xor__(self, X):
        """
        Returns the symmetric difference of ``self`` and ``X``.

        EXAMPLES::

            sage: X = Set([1,2,3,4])
            sage: Y = Set([1,2])
            sage: X.symmetric_difference(Y)
            {3, 4}
            sage: X.__xor__(Y)
            {3, 4}
        """
        return self.symmetric_difference(X)

    def cardinality(self):
        """
        Return the cardinality of this set, which is either an integer or
        ``Infinity``.

        EXAMPLES::

            sage: Set(ZZ).cardinality()
            +Infinity
            sage: Primes().cardinality()
            +Infinity
            sage: Set(GF(5)).cardinality()
            5
            sage: Set(GF(5^2,'a')).cardinality()
            25
        """
        try:
            if not self.is_finite():
                return sage.rings.infinity.infinity
        except (AttributeError, NotImplementedError):
            pass

        if self is not self.__object:
            try:
                return self.__object.cardinality()
            except (AttributeError, NotImplementedError):
                pass
            from sage.rings.integer import Integer
            try:
                return Integer(len(self.__object))
            except TypeError:
                pass

        raise NotImplementedError("computation of cardinality of %s not yet implemented"%self.__object)

    def is_empty(self):
        """
        Return boolean representing emptiness of the set.

        OUTPUT:

        True if the set is empty, false if otherwise.

        EXAMPLES::

            sage: Set([]).is_empty()
            True
            sage: Set([0]).is_empty()
            False
            sage: Set([1..100]).is_empty()
            False
            sage: Set(SymmetricGroup(2).list()).is_empty()
            False
            sage: Set(ZZ).is_empty()
            False

        TESTS::

            sage: Set([]).is_empty()
            True
            sage: Set([1,2,3]).is_empty()
            False
            sage: Set([1..100]).is_empty()
            False
            sage: Set(DihedralGroup(4).list()).is_empty()
            False
            sage: Set(QQ).is_empty()
            False
        """
        return not self.__nonzero__()

    def is_finite(self):
        """
        Return ``True`` if ``self`` is finite.

        EXAMPLES::

            sage: Set(QQ).is_finite()
            False
            sage: Set(GF(250037)).is_finite()
            True
            sage: Set(Integers(2^1000000)).is_finite()
            True
            sage: Set([1,'a',ZZ]).is_finite()
            True
        """
        if isinstance(self.__object, (set, frozenset, tuple, list)):
            return True
        else:
            return self.__object.is_finite()

    def object(self):
        """
        Return underlying object.

        EXAMPLES::

            sage: X = Set(QQ)
            sage: X.object()
            Rational Field
            sage: X = Primes()
            sage: X.object()
            Set of all prime numbers: 2, 3, 5, 7, ...
        """
        return self.__object

    def subsets(self,size=None):
        """
        Return the :class:`Subsets` object representing the subsets of a set.
        If size is specified, return the subsets of that size.

        EXAMPLES::

            sage: X = Set([1,2,3])
            sage: list(X.subsets())
            [{}, {1}, {2}, {3}, {1, 2}, {1, 3}, {2, 3}, {1, 2, 3}]
            sage: list(X.subsets(2))
            [{1, 2}, {1, 3}, {2, 3}]

        """
        from sage.combinat.subset import Subsets
        return Subsets(self,size)

class Set_object_enumerated(Set_object):
    """
    A finite enumerated set.
    """
    def __init__(self, X):
        """
        Initialize ``self``.

        EXAMPLES::

            sage: S = Set(GF(19)); S
            {0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18}
            sage: print latex(S)
            \left\{0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18\right\}
            sage: TestSuite(S).run()
        """
        Set_object.__init__(self, X)

    def is_finite(self):
        r"""
        Return ``True`` as this is a finite set.

        EXAMPLES::

            sage: Set(GF(19)).is_finite()
            True
        """
        return True

    def cardinality(self):
        """
        Return the cardinality of ``self``.

        EXAMPLES::

            sage: Set([1,1]).cardinality()
            1
        """
        from sage.rings.integer import Integer
        return Integer(len(self.set()))

    def __len__(self):
        """
        EXAMPLES::

            sage: len(Set([1,1]))
            1
        """
        return len(self.set())

    def __iter__(self):
        r"""
        Iterating through the elements of ``self``.

        EXAMPLES::

            sage: S = Set(GF(19))
            sage: I = iter(S)
            sage: next(I)
            0
            sage: next(I)
            1
            sage: next(I)
            2
            sage: next(I)
            3
        """
        return iter(self.set())

    def _latex_(self):
        r"""
        Return the LaTeX representation of ``self``.

        EXAMPLES::

            sage: S = Set(GF(2))
            sage: latex(S)
            \left\{0, 1\right\}
        """
        return '\\left\\{' + ', '.join([latex(x) for x in self.set()])  + '\\right\\}'

    def _repr_(self):
        r"""
        Return the string representation of ``self``.

        EXAMPLES::

            sage: S = Set(GF(2))
            sage: S
            {0, 1}
        """
        s = repr(self.set())
        return "{" + s[5:-2] + "}"

    def list(self):
        """
        Return the elements of ``self``, as a list.

        EXAMPLES::

            sage: X = Set(GF(8,'c'))
            sage: X
            {0, 1, c, c + 1, c^2, c^2 + 1, c^2 + c, c^2 + c + 1}
            sage: X.list()
            [0, 1, c, c + 1, c^2, c^2 + 1, c^2 + c, c^2 + c + 1]
            sage: type(X.list())
            <type 'list'>

        .. TODO::

            FIXME: What should be the order of the result?
            That of ``self.object()``? Or the order given by
            ``set(self.object())``? Note that :meth:`__getitem__` is
            currently implemented in term of this list method, which
            is really inefficient ...
        """
        return list(set(self.object()))

    def set(self):
        """
        Return the Python set object associated to this set.

        Python has a notion of finite set, and often Sage sets
        have an associated Python set.  This function returns
        that set.

        EXAMPLES::

            sage: X = Set(GF(8,'c'))
            sage: X
            {0, 1, c, c + 1, c^2, c^2 + 1, c^2 + c, c^2 + c + 1}
            sage: X.set()
            {0, 1, c, c + 1, c^2, c^2 + 1, c^2 + c, c^2 + c + 1}
            sage: type(X.set())
            <type 'set'>
            sage: type(X)
            <class 'sage.sets.set.Set_object_enumerated_with_category'>
        """
        return set(self.object())

    def frozenset(self):
        """
        Return the Python frozenset object associated to this set,
        which is an immutable set (hence hashable).

        EXAMPLES::

            sage: X = Set(GF(8,'c'))
            sage: X
            {0, 1, c, c + 1, c^2, c^2 + 1, c^2 + c, c^2 + c + 1}
            sage: s = X.set(); s
            {0, 1, c, c + 1, c^2, c^2 + 1, c^2 + c, c^2 + c + 1}
            sage: hash(s)
            Traceback (most recent call last):
            ...
            TypeError: unhashable type: 'set'
            sage: s = X.frozenset(); s
            frozenset({0, 1, c, c + 1, c^2, c^2 + 1, c^2 + c, c^2 + c + 1})
            sage: hash(s)
            -1390224788            # 32-bit
             561411537695332972    # 64-bit
            sage: type(s)
            <type 'frozenset'>
        """
        return frozenset(self.object())

    def __hash__(self):
        """
        Return the hash of ``self`` (as a ``frozenset``).

        EXAMPLES::

            sage: s = Set(GF(8,'c'))
            sage: hash(s) == hash(s)
            True
        """
        return hash(self.frozenset())

    def __cmp__(self, other):
        """
        Compare the sets ``self`` and ``other``.

        EXAMPLES::

            sage: X = Set(GF(8,'c'))
            sage: X == Set(GF(8,'c'))
            True
            sage: X == Set(GF(4,'a'))
            False
            sage: Set(QQ) == Set(ZZ)
            False
        """
        if isinstance(other, Set_object_enumerated):
            if self.set() == other.set():
                return 0
            return -1
        else:
            return Set_object.__cmp__(self, other)

    def issubset(self, other):
        r"""
        Return whether ``self`` is a subset of ``other``.

        INPUT:

         - ``other`` -- a finite Set

        EXAMPLES::

            sage: X = Set([1,3,5])
            sage: Y = Set([0,1,2,3,5,7])
            sage: X.issubset(Y)
            True
            sage: Y.issubset(X)
            False
            sage: X.issubset(X)
            True

        TESTS::

            sage: len([Z for Z in Y.subsets() if Z.issubset(X)])
            8
        """
        if not isinstance(other, Set_object_enumerated):
            raise NotImplementedError
        return self.set().issubset(other.set())

    def issuperset(self, other):
        r"""
        Return whether ``self`` is a superset of ``other``.

        INPUT:

         - ``other`` -- a finite Set

        EXAMPLES::

            sage: X = Set([1,3,5])
            sage: Y = Set([0,1,2,3,5])
            sage: X.issuperset(Y)
            False
            sage: Y.issuperset(X)
            True
            sage: X.issuperset(X)
            True

        TESTS::

            sage: len([Z for Z in Y.subsets() if Z.issuperset(X)])
            4
        """
        if not isinstance(other, Set_object_enumerated):
            raise NotImplementedError
        return self.set().issuperset(other.set())

    def union(self, other):
        """
        Return the union of ``self`` and ``other``.

        EXAMPLES::

            sage: X = Set(GF(8,'c'))
            sage: Y = Set([GF(8,'c').0, 1, 2, 3])
            sage: X
            {0, 1, c, c + 1, c^2, c^2 + 1, c^2 + c, c^2 + c + 1}
            sage: Y
            {1, c, 3, 2}
            sage: X.union(Y)
            {0, 1, c, c + 1, c^2, c^2 + 1, c^2 + c, c^2 + c + 1, 2, 3}
        """
        if not isinstance(other, Set_object_enumerated):
            return Set_object.union(self, other)
        return Set_object_enumerated(self.set().union(other.set()))

    def intersection(self, other):
        """
        Return the intersection of ``self`` and ``other``.

        EXAMPLES::

            sage: X = Set(GF(8,'c'))
            sage: Y = Set([GF(8,'c').0, 1, 2, 3])
            sage: X.intersection(Y)
            {1, c}
        """
        if not isinstance(other, Set_object_enumerated):
            return Set_object.intersection(self, other)
        return Set_object_enumerated(self.set().intersection(other.set()))

    def difference(self, other):
        """
        Return the set difference ``self - other``.

        EXAMPLES::

            sage: X = Set([1,2,3,4])
            sage: Y = Set([1,2])
            sage: X.difference(Y)
            {3, 4}
            sage: Z = Set(ZZ)
            sage: W = Set([2.5, 4, 5, 6])
            sage: W.difference(Z)
            {2.50000000000000}
        """
        if not isinstance(other, Set_object_enumerated):
            return Set([x for x in self if x not in other])
        return Set_object_enumerated(self.set().difference(other.set()))

    def symmetric_difference(self, other):
        """
        Return the symmetric difference of ``self`` and ``other``.

        EXAMPLES::

            sage: X = Set([1,2,3,4])
            sage: Y = Set([1,2])
            sage: X.symmetric_difference(Y)
            {3, 4}
            sage: Z = Set(ZZ)
            sage: W = Set([2.5, 4, 5, 6])
            sage: U = W.symmetric_difference(Z)
            sage: 2.5 in U
            True
            sage: 4 in U
            False
            sage: V = Z.symmetric_difference(W)
            sage: V == U
            True
            sage: 2.5 in V
            True
            sage: 6 in V
            False
        """
        if not isinstance(other, Set_object_enumerated):
            return Set_object.symmetric_difference(self, other)
        return Set_object_enumerated(self.set().symmetric_difference(other.set()))

class Set_object_binary(Set_object):
    r"""
    An abstract common base class for sets defined by a binary operation (ex.
    :class:`Set_object_union`, :class:`Set_object_intersection`,
    :class:`Set_object_difference`, and
    :class:`Set_object_symmetric_difference`).

    INPUT:

    - ``X``, ``Y`` -- sets, the operands to ``op``

    - ``op`` -- a string describing the binary operation

    - ``latex_op`` -- a string used for rendering this object in LaTeX

    EXAMPLES::

        sage: X = Set(QQ^2)
        sage: Y = Set(ZZ)
        sage: from sage.sets.set import Set_object_binary
        sage: S = Set_object_binary(X, Y, "union", "\\cup"); S
        Set-theoretic union of Set of elements of Vector space of dimension 2
         over Rational Field and Set of elements of Integer Ring
    """
    def __init__(self, X, Y, op, latex_op):
        r"""
        Initialization.

        TESTS::

            sage: from sage.sets.set import Set_object_binary
            sage: X = Set(QQ^2)
            sage: Y = Set(ZZ)
            sage: S = Set_object_binary(X, Y, "union", "\\cup")
            sage: type(S)
            <class 'sage.sets.set.Set_object_binary_with_category'>
        """
        self._X = X
        self._Y = Y
        self._op = op
        self._latex_op = latex_op
        Set_object.__init__(self, self)

    def _repr_(self):
        r"""
        Return a string representation of this set.

        EXAMPLES::

            sage: Set(ZZ).union(Set(GF(5)))
            Set-theoretic union of Set of elements of Integer Ring and {0, 1, 2, 3, 4}
        """
        return "Set-theoretic {} of {} and {}".format(self._op, self._X, self._Y)

    def _latex_(self):
        r"""
        Return a latex representation of this set.

        EXAMPLES::

            sage: latex(Set(ZZ).union(Set(GF(5))))
            \Bold{Z} \cup \left\{0, 1, 2, 3, 4\right\}
        """
        return latex(self._X) + self._latex_op + latex(self._Y)

    def __hash__(self):
        """
        The hash value of this set.

        EXAMPLES:

        The hash values of equal sets are in general not equal since it is not
        decidable whether two sets are equal::

            sage: X = Set(GF(13)).intersection(Set(ZZ))
            sage: Y = Set(ZZ).intersection(Set(GF(13)))
            sage: hash(X) == hash(Y)
            False

        TESTS:

        Test that :trac:`14432` has been resolved::

            sage: S = Set(ZZ).union(Set([infinity]))
            sage: T = Set(ZZ).union(Set([infinity]))
            sage: hash(S) == hash(T)
            True
        """
        return hash((self._X, self._Y, self._op))

class Set_object_union(Set_object_binary):
    """
    A formal union of two sets.
    """
    def __init__(self, X, Y):
        r"""
        Initialize ``self``.

        EXAMPLES::

            sage: S = Set(QQ^2)
            sage: T = Set(ZZ)
            sage: X = S.union(T); X
            Set-theoretic union of Set of elements of Vector space of dimension 2 over Rational Field and Set of elements of Integer Ring

            sage: latex(X)
            \Bold{Q}^{2} \cup \Bold{Z}

            sage: TestSuite(X).run()
        """
        Set_object_binary.__init__(self, X, Y, "union", "\\cup")

    def is_finite(self):
        r"""
        Return whether this set is finite.

        EXAMPLES::

            sage: X = Set(range(10))
            sage: Y = Set(range(-10,0))
            sage: Z = Set(Primes())
            sage: X.union(Y).is_finite()
            True
            sage: X.union(Z).is_finite()
            False
        """
        return self._X.is_finite() and self._Y.is_finite()

    def __cmp__(self, right):
        r"""
        Try to compare ``self`` and ``right``.

        .. NOTE::

           Comparison is basically not implemented, or rather it could
           say sets are not equal even though they are.  I don't know
           how one could implement this for a generic union of sets in
           a meaningful manner.  So be careful when using this.

        EXAMPLES::

            sage: Y = Set(ZZ^2).union(Set(ZZ^3))
            sage: X = Set(ZZ^3).union(Set(ZZ^2))
            sage: X == Y
            True
            sage: Y == X
            True

        This illustrates that equality testing for formal unions
        can be misleading in general.

        ::

            sage: Set(ZZ).union(Set(QQ)) == Set(QQ)
            False
        """
        if not is_Set(right):
            return -1
        if not isinstance(right, Set_object_union):
            return -1
        if self._X == right._X and self._Y == right._Y or \
           self._X == right._Y and self._Y == right._X:
            return 0
        return -1

    def __iter__(self):
        """
        Return iterator over the elements of ``self``.

        EXAMPLES::

            sage: [x for x in Set(GF(3)).union(Set(GF(2)))]
            [0, 1, 2, 0, 1]
        """
        for x in self._X:
            yield x
        for y in self._Y:
            yield y

    def __contains__(self, x):
        """
        Return ``True`` if ``x`` is an element of ``self``.

        EXAMPLES::

            sage: X = Set(GF(3)).union(Set(GF(2)))
            sage: GF(5)(1) in X
            False
            sage: GF(3)(2) in X
            True
            sage: GF(2)(0) in X
            True
            sage: GF(5)(0) in X
            False
        """
        return x in self._X or x in self._Y

    def cardinality(self):
        """
        Return the cardinality of this set.

        EXAMPLES::

            sage: X = Set(GF(3)).union(Set(GF(2)))
            sage: X
            {0, 1, 2, 0, 1}
            sage: X.cardinality()
            5

            sage: X = Set(GF(3)).union(Set(ZZ))
            sage: X.cardinality()
            +Infinity
        """
        return self._X.cardinality() + self._Y.cardinality()

class Set_object_intersection(Set_object_binary):
    """
    Formal intersection of two sets.
    """
    def __init__(self, X, Y):
        r"""
        Initialize ``self``.

        EXAMPLES::

            sage: S = Set(QQ^2)
            sage: T = Set(ZZ)
            sage: X = S.intersection(T); X
            Set-theoretic intersection of Set of elements of Vector space of dimension 2 over Rational Field and Set of elements of Integer Ring
            sage: latex(X)
            \Bold{Q}^{2} \cap \Bold{Z}

            sage: X = Set(IntegerRange(100)).intersection(Primes())
            sage: X.is_finite()
            True
            sage: TestSuite(X).run()
        """
        Set_object_binary.__init__(self, X, Y, "intersection", "\\cap")

    def is_finite(self):
        r"""
        Return whether this set is finite.

        EXAMPLES::

            sage: X = Set(IntegerRange(100))
            sage: Y = Set(ZZ)
            sage: X.intersection(Y).is_finite()
            True
            sage: Y.intersection(X).is_finite()
            True
            sage: Y.intersection(Set(QQ)).is_finite()
            Traceback (most recent call last):
            ...
            NotImplementedError
        """
        if self._X.is_finite():
            return True
        elif self._Y.is_finite():
            return True
        raise NotImplementedError

    def __cmp__(self, right):
        r"""
        Try to compare ``self`` and ``right``.

        .. NOTE::

           Comparison is basically not implemented, or rather it could
           say sets are not equal even though they are.  I don't know
           how one could implement this for a generic intersection of
           sets in a meaningful manner.  So be careful when using this.

        EXAMPLES::

            sage: Y = Set(ZZ).intersection(Set(QQ))
            sage: X = Set(QQ).intersection(Set(ZZ))
            sage: X == Y
            True
            sage: Y == X
            True

        This illustrates that equality testing for formal unions
        can be misleading in general.

        ::

            sage: Set(ZZ).intersection(Set(QQ)) == Set(QQ)
            False
        """
        if not is_Set(right):
            return -1
        if not isinstance(right, Set_object_intersection):
            return -1
        if self._X == right._X and self._Y == right._Y or \
           self._X == right._Y and self._Y == right._X:
            return 0
        return -1

    def __iter__(self):
        """
        Return iterator through elements of ``self``.

        ``self`` is a formal intersection of `X` and `Y` and this function is
        implemented by iterating through the elements of `X` and for
        each checking if it is in `Y`, and if yielding it.

        EXAMPLES::

            sage: X = Set(ZZ).intersection(Primes())
            sage: I = X.__iter__()
            sage: next(I)
            2

        Check that known finite intersections have finite iterators (see
        :trac:`18159`)::

            sage: P = Set(ZZ).intersection(Set(range(10,20)))
            sage: list(P)
            [10, 11, 12, 13, 14, 15, 16, 17, 18, 19]
        """
        X = self._X
        Y = self._Y
        if not self._X.is_finite() and self._Y.is_finite():
            X,Y = Y,X
        for x in X:
            if x in Y:
                yield x

    def __contains__(self, x):
        """
        Return ``True`` if ``self`` contains ``x``.

        Since ``self`` is a formal intersection of `X` and `Y` this function
        returns ``True`` if both `X` and `Y` contains ``x``.

        EXAMPLES::

            sage: X = Set(QQ).intersection(Set(RR))
            sage: 5 in X
            True
            sage: ComplexField().0 in X
            False

        Any specific floating-point number in Sage is to finite precision,
        hence it is rational::

            sage: RR(sqrt(2)) in X
            True

        Real constants are not rational::

            sage: pi in X
            False
        """
        return x in self._X and x in self._Y

class Set_object_difference(Set_object_binary):
    """
    Formal difference of two sets.
    """
    def __init__(self, X, Y):
        r"""
        Initialize ``self``.

        EXAMPLES::

            sage: S = Set(QQ)
            sage: T = Set(ZZ)
            sage: X = S.difference(T); X
            Set-theoretic difference of Set of elements of Rational Field and Set of elements of Integer Ring
            sage: latex(X)
            \Bold{Q} - \Bold{Z}

            sage: TestSuite(X).run()
        """
        Set_object_binary.__init__(self, X, Y, "difference", "-")

    def is_finite(self):
        r"""
        Return whether this set is finite.

        EXAMPLES::

            sage: X = Set(range(10))
            sage: Y = Set(range(-10,5))
            sage: Z = Set(QQ)
            sage: X.difference(Y).is_finite()
            True
            sage: X.difference(Z).is_finite()
            True
            sage: Z.difference(X).is_finite()
            False
            sage: Z.difference(Set(ZZ)).is_finite()
            Traceback (most recent call last):
            ...
            NotImplementedError
        """
        if self._X.is_finite():
            return True
        elif self._Y.is_finite():
            return False
        raise NotImplementedError

    def __cmp__(self, right):
        r"""
        Try to compare ``self`` and ``right``.

        .. NOTE::

           Comparison is basically not implemented, or rather it could
           say sets are not equal even though they are.  I don't know
           how one could implement this for a generic intersection of
           sets in a meaningful manner.  So be careful when using
           this.

        EXAMPLES::

            sage: Y = Set(ZZ).difference(Set(QQ))
            sage: Y == Set([])
            False
            sage: X = Set(QQ).difference(Set(ZZ))
            sage: Y == X
            False
            sage: Z = X.difference(Set(ZZ))
            sage: Z == X
            False

        This illustrates that equality testing for formal unions
        can be misleading in general.

        ::

            sage: X == Set(QQ).difference(Set(ZZ))
            True
        """
        if not is_Set(right):
            return -1
        if not isinstance(right, Set_object_difference):
            return -1
        if self._X == right._X and self._Y == right._Y: 
            return 0
        return -1

    def __iter__(self):
        """
        Return iterator through elements of ``self``.

        ``self`` is a formal difference of `X` and `Y` and this function
        is implemented by iterating through the elements of `X` and for
        each checking if it is not in `Y`, and if yielding it.

        EXAMPLES::

            sage: X = Set(ZZ).difference(Primes())
            sage: I = X.__iter__()
            sage: next(I)
            0
            sage: next(I)
            1
            sage: next(I)
            -1
            sage: next(I)
            -2
            sage: next(I)
            -3
        """
        for x in self._X:
            if x not in self._Y:
                yield x

    def __contains__(self, x):
        """
        Return ``True`` if ``self`` contains ``x``.

        Since ``self`` is a formal intersection of `X` and `Y` this function
        returns ``True`` if both `X` and `Y` contains ``x``.

        EXAMPLES::

            sage: X = Set(QQ).difference(Set(ZZ))
            sage: 5 in X
            False
            sage: ComplexField().0 in X
            False
            sage: sqrt(2) in X     # since sqrt(2) is not a numerical approx
            False
            sage: sqrt(RR(2)) in X # since sqrt(RR(2)) is a numerical approx
            True
            sage: 5/2 in X
            True
        """
        return x in self._X and x not in self._Y

class Set_object_symmetric_difference(Set_object_binary):
    """
    Formal symmetric difference of two sets.
    """
    def __init__(self, X, Y):
        r"""
        Initialize ``self``.

        EXAMPLES::

            sage: S = Set(QQ)
            sage: T = Set(ZZ)
            sage: X = S.symmetric_difference(T); X
            Set-theoretic symmetric difference of Set of elements of Rational Field and Set of elements of Integer Ring
            sage: latex(X)
            \Bold{Q} \bigtriangleup \Bold{Z}

            sage: TestSuite(X).run()
        """
        Set_object_binary.__init__(self, X, Y, "symmetric difference", "\\bigtriangleup")

    def is_finite(self):
        r"""
        Return whether this set is finite.

        EXAMPLES::

            sage: X = Set(range(10))
            sage: Y = Set(range(-10,5))
            sage: Z = Set(QQ)
            sage: X.symmetric_difference(Y).is_finite()
            True
            sage: X.symmetric_difference(Z).is_finite()
            False
            sage: Z.symmetric_difference(X).is_finite()
            False
            sage: Z.symmetric_difference(Set(ZZ)).is_finite()
            Traceback (most recent call last):
            ...
            NotImplementedError
        """
        if self._X.is_finite():
            return self._Y.is_finite()
        elif self._Y.is_finite():
            return False
        raise NotImplementedError

    def __cmp__(self, right):
        r"""
        Try to compare ``self`` and ``right``.

        .. NOTE::

           Comparison is basically not implemented, or rather it could
           say sets are not equal even though they are.  I don't know
           how one could implement this for a generic symmetric
           difference of sets in a meaningful manner.  So be careful
           when using this.

        EXAMPLES::

            sage: Y = Set(ZZ).symmetric_difference(Set(QQ))
            sage: X = Set(QQ).symmetric_difference(Set(ZZ))
            sage: X == Y
            True
            sage: Y == X
            True

        """
        if not is_Set(right):
            return -1
        if not isinstance(right, Set_object_symmetric_difference):
            return -1
        if self._X == right._X and self._Y == right._Y or \
           self._X == right._Y and self._Y == right._X:
            return 0
        return -1

    def __iter__(self):
        """
        Return iterator through elements of ``self``.

        This function is implemented by first iterating through the elements
        of `X` and  yielding it if it is not in `Y`.
        Then it will iterate throw all the elements of `Y` and yielding it if
        it is not in `X`.

        EXAMPLES::

            sage: X = Set(ZZ).symmetric_difference(Primes())
            sage: I = X.__iter__()
            sage: next(I)
            0
            sage: next(I)
            1
            sage: next(I)
            -1
            sage: next(I)
            -2
            sage: next(I)
            -3
        """
        for x in self._X:
            if x not in self._Y:
                yield x

        for y in self._Y:
            if y not in self._X:
                yield y

    def __contains__(self, x):
        """
        Return ``True`` if ``self`` contains ``x``.

        Since ``self`` is the formal symmetric difference of `X` and `Y`
        this function returns ``True`` if either `X` or `Y` (but not both)
        contains ``x``.

        EXAMPLES::

            sage: X = Set(QQ).symmetric_difference(Primes())
            sage: 4 in X
            True
            sage: ComplexField().0 in X
            False
            sage: sqrt(2) in X      # since sqrt(2) is currently symbolic
            False
            sage: sqrt(RR(2)) in X # since sqrt(RR(2)) is currently approximated
            True
            sage: pi in X
            False
            sage: 5/2 in X
            True
            sage: 3 in X
            False
        """
        return (x in self._X and x not in self._Y) \
               or (x in self._Y and x not in self._X)
