code: def collect_variables(self, g_scope='gen', d_scope='discrim'):
          
          self.g_vars = tf.get_collection(tf.GraphKeys.TRAINABLE_VARIABLES, g_scope)
          assert self.g_vars
          self.d_vars = tf.get_collection(tf.GraphKeys.TRAINABLE_VARIABLES, d_scope)
          assert self.d_vars
docs: Assign `self.g_vars` to the parameters under scope `g_scope`,
          and same with `self.d_vars`.