def get_possible_actions(self):
<EOL>if self.possible_actions is None:<EOL><INDENT>raise ValueError("<STR_LIT>")<EOL><DEDENT>return self.possible_actions<EOL>
Return a sequence containing the possible actions that can be
        executed within the environment. Raise a ValueError if possible
        actions were not provided at initialization.

        Usage:
            possible_actions = scenario.get_possible_actions()

        Arguments: None
        Return:
            A sequence containing the possible actions which can be
            executed within this scenario.