<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def create_class_from_xml_string(target_class, xml_string):
 """Creates an instance of the target class from a string. :param target_class: The class which will be instantiated and populated with the contents of the XML. This class must have a c_tag and a c_namespace class variable. :param xml_string: A string which contains valid XML. The root element of the XML string should match the tag and namespace of the desired class. :return: An instance of the target class with members assigned according to the contents of the XML - or None if the root XML tag and namespace did not match those of the target class. """

    if not isinstance(xml_string, six.binary_type):
        xml_string = xml_string.encode('utf-8')
    tree = defusedxml.ElementTree.fromstring(xml_string)
    return create_class_from_element_tree(target_class, tree)