human
Complete this python program:
def _resp_app_iter_property():
assistant
#Here is the Python program you requested.

    """Set and retrieve Response.app_iter
    Mostly a pass-through to Response._app_iter; it\s a property so it can zero
    out an existing content-length on assignment.
    """
    def getter(self):
        return self._app_iter
    def setter(self, value):
        if isinstance(value, (list, tuple)):
            self.content_length = sum(map(len, value))
        elif (value is not None):
            self.content_length = None
            self._body = None
        self._app_iter = value
    return property(getter, setter, doc='Retrieve    and    set    the    response    app_iter')