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diff --git a/src/blinker/_saferef.py b/src/blinker/_saferef.py
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+# extracted from Louie, http://pylouie.org/
+# updated for Python 3
+#
+# Copyright (c) 2006 Patrick K. O'Brien, Mike C. Fletcher,
+#                    Matthew R. Scott
+#
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions are
+# met:
+#
+#     * Redistributions of source code must retain the above copyright
+#       notice, this list of conditions and the following disclaimer.
+#
+#     * Redistributions in binary form must reproduce the above
+#       copyright notice, this list of conditions and the following
+#       disclaimer in the documentation and/or other materials provided
+#       with the distribution.
+#
+#     * Neither the name of the <ORGANIZATION> nor the names of its
+#       contributors may be used to endorse or promote products derived
+#       from this software without specific prior written permission.
+#
+# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+# A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+# OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+# DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+# THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+# OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+#
+"""Refactored 'safe reference from dispatcher.py"""
+import operator
+import sys
+import traceback
+import weakref
+
+
+get_self = operator.attrgetter("__self__")
+get_func = operator.attrgetter("__func__")
+
+
+def safe_ref(target, on_delete=None):
+    """Return a *safe* weak reference to a callable target.
+
+    - ``target``: The object to be weakly referenced, if it's a bound
+      method reference, will create a BoundMethodWeakref, otherwise
+      creates a simple weakref.
+
+    - ``on_delete``: If provided, will have a hard reference stored to
+      the callable to be called after the safe reference goes out of
+      scope with the reference object, (either a weakref or a
+      BoundMethodWeakref) as argument.
+    """
+    try:
+        im_self = get_self(target)
+    except AttributeError:
+        if callable(on_delete):
+            return weakref.ref(target, on_delete)
+        else:
+            return weakref.ref(target)
+    else:
+        if im_self is not None:
+            # Turn a bound method into a BoundMethodWeakref instance.
+            # Keep track of these instances for lookup by disconnect().
+            assert hasattr(target, "im_func") or hasattr(target, "__func__"), (
+                f"safe_ref target {target!r} has im_self, but no im_func, "
+                "don't know how to create reference"
+            )
+            reference = BoundMethodWeakref(target=target, on_delete=on_delete)
+            return reference
+
+
+class BoundMethodWeakref:
+    """'Safe' and reusable weak references to instance methods.
+
+    BoundMethodWeakref objects provide a mechanism for referencing a
+    bound method without requiring that the method object itself
+    (which is normally a transient object) is kept alive.  Instead,
+    the BoundMethodWeakref object keeps weak references to both the
+    object and the function which together define the instance method.
+
+    Attributes:
+
+    - ``key``: The identity key for the reference, calculated by the
+      class's calculate_key method applied to the target instance method.
+
+    - ``deletion_methods``: Sequence of callable objects taking single
+      argument, a reference to this object which will be called when
+      *either* the target object or target function is garbage
+      collected (i.e. when this object becomes invalid).  These are
+      specified as the on_delete parameters of safe_ref calls.
+
+    - ``weak_self``: Weak reference to the target object.
+
+    - ``weak_func``: Weak reference to the target function.
+
+    Class Attributes:
+
+    - ``_all_instances``: Class attribute pointing to all live
+      BoundMethodWeakref objects indexed by the class's
+      calculate_key(target) method applied to the target objects.
+      This weak value dictionary is used to short-circuit creation so
+      that multiple references to the same (object, function) pair
+      produce the same BoundMethodWeakref instance.
+    """
+
+    _all_instances = weakref.WeakValueDictionary()
+
+    def __new__(cls, target, on_delete=None, *arguments, **named):
+        """Create new instance or return current instance.
+
+        Basically this method of construction allows us to
+        short-circuit creation of references to already-referenced
+        instance methods.  The key corresponding to the target is
+        calculated, and if there is already an existing reference,
+        that is returned, with its deletion_methods attribute updated.
+        Otherwise the new instance is created and registered in the
+        table of already-referenced methods.
+        """
+        key = cls.calculate_key(target)
+        current = cls._all_instances.get(key)
+        if current is not None:
+            current.deletion_methods.append(on_delete)
+            return current
+        else:
+            base = super().__new__(cls)
+            cls._all_instances[key] = base
+            base.__init__(target, on_delete, *arguments, **named)
+            return base
+
+    def __init__(self, target, on_delete=None):
+        """Return a weak-reference-like instance for a bound method.
+
+        - ``target``: The instance-method target for the weak reference,
+          must have im_self and im_func attributes and be
+          reconstructable via the following, which is true of built-in
+          instance methods::
+
+            target.im_func.__get__( target.im_self )
+
+        - ``on_delete``: Optional callback which will be called when
+          this weak reference ceases to be valid (i.e. either the
+          object or the function is garbage collected).  Should take a
+          single argument, which will be passed a pointer to this
+          object.
+        """
+
+        def remove(weak, self=self):
+            """Set self.isDead to True when method or instance is destroyed."""
+            methods = self.deletion_methods[:]
+            del self.deletion_methods[:]
+            try:
+                del self.__class__._all_instances[self.key]
+            except KeyError:
+                pass
+            for function in methods:
+                try:
+                    if callable(function):
+                        function(self)
+                except Exception:
+                    try:
+                        traceback.print_exc()
+                    except AttributeError:
+                        e = sys.exc_info()[1]
+                        print(
+                            f"Exception during saferef {self} "
+                            f"cleanup function {function}: {e}"
+                        )
+
+        self.deletion_methods = [on_delete]
+        self.key = self.calculate_key(target)
+        im_self = get_self(target)
+        im_func = get_func(target)
+        self.weak_self = weakref.ref(im_self, remove)
+        self.weak_func = weakref.ref(im_func, remove)
+        self.self_name = str(im_self)
+        self.func_name = str(im_func.__name__)
+
+    def calculate_key(cls, target):
+        """Calculate the reference key for this reference.
+
+        Currently this is a two-tuple of the id()'s of the target
+        object and the target function respectively.
+        """
+        return (id(get_self(target)), id(get_func(target)))
+
+    calculate_key = classmethod(calculate_key)
+
+    def __str__(self):
+        """Give a friendly representation of the object."""
+        return "{}({}.{})".format(
+            self.__class__.__name__,
+            self.self_name,
+            self.func_name,
+        )
+
+    __repr__ = __str__
+
+    def __nonzero__(self):
+        """Whether we are still a valid reference."""
+        return self() is not None
+
+    def __cmp__(self, other):
+        """Compare with another reference."""
+        if not isinstance(other, self.__class__):
+            return cmp(self.__class__, type(other))
+        return cmp(self.key, other.key)
+
+    def __call__(self):
+        """Return a strong reference to the bound method.
+
+        If the target cannot be retrieved, then will return None,
+        otherwise returns a bound instance method for our object and
+        function.
+
+        Note: You may call this method any number of times, as it does
+        not invalidate the reference.
+        """
+        target = self.weak_self()
+        if target is not None:
+            function = self.weak_func()
+            if function is not None:
+                return function.__get__(target)
+        return None