<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def safe_str_to_class(s):
 """Helper function to map string class names to module classes."""

    lst = s.split(".")
    klass = lst[-1]
    mod_list = lst[:-1]
    module = ".".join(mod_list)

    # ruby compatibility kludge: resque sends just a class name and
    # not a module name so if I use resque to queue a ruby class
    # called "Worker" then pyres will throw a "ValueError: Empty
    # module name" exception.  To avoid that, if there's no module in
    # the json then we'll use the classname as a module name.
    if not module:
        module = klass

    mod = my_import(module)
    if hasattr(mod, klass):
        return getattr(mod, klass)
    else:
        raise ImportError('')