def __new__( cls, target, onDelete=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
        deletionMethods attribute updated.  Otherwise the
        new instance is created and registered in the table
        of already-referenced methods.
        """
        key = cls.calculateKey(target)
        current =cls._allInstances.get(key)
        if current is not None:
            current.deletionMethods.append( onDelete)
            return current
        else:
            base = super( BoundMethodWeakref, cls).__new__( cls )
            cls._allInstances[key] = base
            base.__init__( target, onDelete, *arguments,**named)
            return base
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
        deletionMethods attribute updated.  Otherwise the
        new instance is created and registered in the table
        of already-referenced methods.
        
stackoverflow/venv/lib/python3.6/site-packages/pydispatch/saferef.py