gistfile1.py

def merge_settings(request_setting, session_setting, dict_class=OrderedDict):
    """
    Determines appropriate setting for a given request, taking into account the setting on that
    request, and the setting in the session. If a setting is a dictionary, they will be merged together
    using `dict_class`
    """

    if session_setting is None:
        return request_setting

    if request_setting is None:
        return session_setting

    # Bypass if not a dictionary (e.g. timeout)
    if (
            not isinstance(session_setting, Mapping) or
            not isinstance(request_setting, Mapping)
    ):
        return request_setting

    merged_setting = dict_class(to_key_val_list(session_setting))
    request_setting = dict_class(to_key_val_list(request_setting))
    
    merged_setting.update(request_setting)

    # Remove keys that are set to None.
    for (k, v) in request_setting.items():
        if v is None:
            del merged_setting[k]

    return merged_setting