"""Weak reference support for Python.

This module is an implementation of PEP 205:

http://www.python.org/dev/peps/pep-0205/

"""

# Naming convention: Variables named "wr" are weak reference objects;

# they are called this instead of "ref" to avoid name collisions with

# the module-global ref() function imported from _weakref.

import UserDict

from _weakref import (

     getweakrefcount,

     getweakrefs,

     ref,

     proxy,

     CallableProxyType,

     ProxyType,

     ReferenceType)

from exceptions import ReferenceError

ProxyTypes = (ProxyType, CallableProxyType)

__all__ = ["ref", "proxy", "getweakrefcount", "getweakrefs",

           "WeakKeyDictionary", "ReferenceError", "ReferenceType", "ProxyType",

           "CallableProxyType", "ProxyTypes", "WeakValueDictionary"]

class WeakValueDictionary(UserDict.UserDict):

    """Mapping class that references values weakly.

    Entries in the dictionary will be discarded when no strong

    reference to the value exists anymore

    """

    # We inherit the constructor without worrying about the input

    # dictionary; since it uses our .update() method, we get the right

    # checks (if the other dictionary is a WeakValueDictionary,

    # objects are unwrapped on the way out, and we always wrap on the

    # way in).

    def __init__(self, *args, **kw):

        def remove(wr, selfref=ref(self)):

            self = selfref()

            if self is not None:

                del self.data[wr.key]

        self._remove = remove

        UserDict.UserDict.__init__(self, *args, **kw)

    def __getitem__(self, key):

        o = self.data[key]()

        if o is None:

            raise KeyError, key

        else:

            return o

    def __contains__(self, key):

        try:

            o = self.data[key]()

        except KeyError:

            return False

        return o is not None

    def has_key(self, key):

        try:

            o = self.data[key]()

        except KeyError:

            return False

        return o is not None

    def __repr__(self):

        return "<WeakValueDictionary at %s>" % id(self)

    def __setitem__(self, key, value):

        self.data[key] = KeyedRef(value, self._remove, key)

    def copy(self):

        new = WeakValueDictionary()

        for key, wr in self.data.items():

            o = wr()

            if o is not None:

                new[key] = o

        return new

    def get(self, key, default=None):

        try:

            wr = self.data[key]

        except KeyError:

            return default

        else:

            o = wr()

            if o is None:

                # This should only happen

                return default

            else:

                return o

    def items(self):

        L = []

        for key, wr in self.data.items():

            o = wr()

            if o is not None:

                L.append((key, o))

        return L

    def iteritems(self):

        for wr in self.data.itervalues():

            value = wr()

            if value is not None:

                yield wr.key, value

    def iterkeys(self):

        return self.data.iterkeys()

    def __iter__(self):

        return self.data.iterkeys()

    def itervaluerefs(self):

        """Return an iterator that yields the weak references to the values.

        The references are not guaranteed to be 'live' at the time

        they are used, so the result of calling the references needs

        to be checked before being used.  This can be used to avoid

        creating references that will cause the garbage collector to

        keep the values around longer than needed.

        """

        return self.data.itervalues()

    def itervalues(self):

        for wr in self.data.itervalues():

            obj = wr()

            if obj is not None:

                yield obj

    def popitem(self):

        while 1:

            key, wr = self.data.popitem()

            o = wr()

            if o is not None:

                return key, o

    def pop(self, key, *args):

        try:

            o = self.data.pop(key)()

        except KeyError:

            if args:

                return args[0]

            raise

        if o is None:

            raise KeyError, key

        else:

            return o

    def setdefault(self, key, default=None):

        try:

            wr = self.data[key]

        except KeyError:

            self.data[key] = KeyedRef(default, self._remove, key)

            return default

        else:

            return wr()

    def update(self, dict=None, **kwargs):

        d = self.data

        if dict is not None:

            if not hasattr(dict, "items"):

                dict = type({})(dict)

            for key, o in dict.items():

                d[key] = KeyedRef(o, self._remove, key)

        if len(kwargs):

            self.update(kwargs)

    def valuerefs(self):

        """Return a list of weak references to the values.

        The references are not guaranteed to be 'live' at the time

        they are used, so the result of calling the references needs

        to be checked before being used.  This can be used to avoid

        creating references that will cause the garbage collector to

        keep the values around longer than needed.

        """

        return self.data.values()

    def values(self):

        L = []

        for wr in self.data.values():

            o = wr()

            if o is not None:

                L.append(o)

        return L

class KeyedRef(ref):

    """Specialized reference that includes a key corresponding to the value.

    This is used in the WeakValueDictionary to avoid having to create

    a function object for each key stored in the mapping.  A shared

    callback object can use the 'key' attribute of a KeyedRef instead

    of getting a reference to the key from an enclosing scope.

    """

    __slots__ = "key",

    def __new__(type, ob, callback, key):

        self = ref.__new__(type, ob, callback)

        self.key = key

        return self

    def __init__(self, ob, callback, key):

        super(KeyedRef,  self).__init__(ob, callback)

class WeakKeyDictionary(UserDict.UserDict):

    """ Mapping class that references keys weakly.

    Entries in the dictionary will be discarded when there is no

    longer a strong reference to the key. This can be used to

    associate additional data with an object owned by other parts of

    an application without adding attributes to those objects. This

    can be especially useful with objects that override attribute

    accesses.

    """

    def __init__(self, dict=None):

        self.data = {}

        def remove(k, selfref=ref(self)):

            self = selfref()

            if self is not None:

                del self.data[k]

        self._remove = remove

        if dict is not None: self.update(dict)

    def __delitem__(self, key):

        del self.data[ref(key)]

    def __getitem__(self, key):

        return self.data[ref(key)]

    def __repr__(self):

        return "<WeakKeyDictionary at %s>" % id(self)

    def __setitem__(self, key, value):

        self.data[ref(key, self._remove)] = value

    def copy(self):

        new = WeakKeyDictionary()

        for key, value in self.data.items():

            o = key()

            if o is not None:

                new[o] = value

        return new

    def get(self, key, default=None):

        return self.data.get(ref(key),default)

    def has_key(self, key):

        try:

            wr = ref(key)

        except TypeError:

            return 0

        return wr in self.data

    def __contains__(self, key):

        try:

            wr = ref(key)

        except TypeError:

            return 0

        return wr in self.data

    def items(self):

        L = []

        for key, value in self.data.items():

            o = key()

            if o is not None:

                L.append((o, value))

        return L

    def iteritems(self):

        for wr, value in self.data.iteritems():

            key = wr()

            if key is not None:

                yield key, value

    def iterkeyrefs(self):

        """Return an iterator that yields the weak references to the keys.

        The references are not guaranteed to be 'live' at the time

        they are used, so the result of calling the references needs

        to be checked before being used.  This can be used to avoid

        creating references that will cause the garbage collector to

        keep the keys around longer than needed.

        """

        return self.data.iterkeys()

    def iterkeys(self):

        for wr in self.data.iterkeys():

            obj = wr()

            if obj is not None:

                yield obj

    def __iter__(self):

        return self.iterkeys()

    def itervalues(self):

        return self.data.itervalues()

    def keyrefs(self):

        """Return a list of weak references to the keys.

        The references are not guaranteed to be 'live' at the time

        they are used, so the result of calling the references needs

        to be checked before being used.  This can be used to avoid

        creating references that will cause the garbage collector to

        keep the keys around longer than needed.

        """

        return self.data.keys()

    def keys(self):

        L = []

        for wr in self.data.keys():

            o = wr()

            if o is not None:

                L.append(o)

        return L

    def popitem(self):

        while 1:

            key, value = self.data.popitem()

            o = key()

            if o is not None:

                return o, value

    def pop(self, key, *args):

        return self.data.pop(ref(key), *args)

    def setdefault(self, key, default=None):

        return self.data.setdefault(ref(key, self._remove),default)

    def update(self, dict=None, **kwargs):

        d = self.data

        if dict is not None:

            if not hasattr(dict, "items"):

                dict = type({})(dict)

            for key, value in dict.items():

                d[ref(key, self._remove)] = value

        if len(kwargs):

            self.update(kwargs)