Convert a string version of a function name to the callable object.

def get_class(class_string):
    """
    Convert a string version of a function name to the callable object.
    """
    try:
        mod_name, class_name = get_mod_func(class_string)
        if class_name != '':
            cls = getattr(__import__(mod_name, {}, {}, ['']), class_name)
            return cls
    except (ImportError, AttributeError):
        pass
    raise ImportError('Failed to import %s' % class_string)