def get_value(self, key):
try:<EOL><INDENT>return self._values[key]<EOL><DEDENT>except KeyError:<EOL><INDENT>return None<EOL><DEDENT>
Retrieves a predicted value.

:param key: A descriptor key for a registered predicted value.
:type key: str
:return: The value stored at the provided descriptor key. None if no key is provided.
:rtype: :class:`PredictedValue`