<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def crud_url_name(model, action, prefix=None):
 """ Returns url name for given model and action. """

    if prefix is None:
        prefix = ""
    app_label = model._meta.app_label
    model_lower = model.__name__.lower()
    return '%s%s_%s_%s' % (prefix, app_label, model_lower, action)