def seed(self, seed=None):
<EOL>if seed is None:<EOL><INDENT>return []<EOL><DEDENT>self.np_random.seed(seed)<EOL>return [seed]<EOL>
Set the seed for this environment's random number generator.

Returns:
    list<bigint>: Returns the list of seeds used in this env's random
      number generators. The first value in the list should be the
      "main" seed, or the value which a reproducer should pass to
      'seed'. Often, the main seed equals the provided 'seed', but
      this won't be true if seed=None, for example.