'Construct a new xmodule
runtime: An XBlock runtime allowing access to external resources
descriptor: the XModuleDescriptor that this module is an instance of.
field_data: A dictionary-like object that maps field names to values
for those fields.'

def __init__(self, descriptor, *args, **kwargs):

    self.descriptor = descriptor
    self._runtime = None
    super(XModule, self).__init__(*args, **kwargs)
    self.runtime.xmodule_instance = self
