Called when a binding is altered.

        - `node` is the statement responsible for the change
        - `value` is the new value, a Binding instance

def addBinding(self, node, value):
        """
        Called when a binding is altered.

        - `node` is the statement responsible for the change
        - `value` is the new value, a Binding instance
        """
        # assert value.source in (node, node.parent):
        for scope in self.scopeStack[::-1]:
            if value.name in scope:
                break
        existing = scope.get(value.name)

        if (existing and not isinstance(existing, Builtin) and
                not self.differentForks(node, existing.source)):

            parent_stmt = self.getParent(value.source)
            if isinstance(existing, Importation) and isinstance(parent_stmt, FOR_TYPES):
                self.report(messages.ImportShadowedByLoopVar,
                            node, value.name, existing.source)

            elif scope is self.scope:
                if (isinstance(parent_stmt, ast.comprehension) and
                        not isinstance(self.getParent(existing.source),
                                       (FOR_TYPES, ast.comprehension))):
                    self.report(messages.RedefinedInListComp,
                                node, value.name, existing.source)
                elif not existing.used and value.redefines(existing):
                    if value.name != '_' or isinstance(existing, Importation):
                        if not is_typing_overload(existing, self.scopeStack):
                            self.report(messages.RedefinedWhileUnused,
                                        node, value.name, existing.source)

            elif isinstance(existing, Importation) and value.redefines(existing):
                existing.redefined.append(node)

        if value.name in self.scope:
            # then assume the rebound name is used as a global or within a loop
            value.used = self.scope[value.name].used

        self.scope[value.name] = value