Issue while trying to train my first chatbot

Hi, i am trying to train my first chatbot. I am using code that was already existing (please see below) i get the following error “could not determine a constructor for the tag 'tag:yaml.org,2002” from rasa_core.agent import Agent from rasa_core.policies.keras_policy import KerasPolicy from rasa_core.policies.memoization import MemoizationPolicy from rasa_core.featurizers import (MaxHistoryTrackerFeaturizer, BinarySingleStateFeaturizer)

if name == ‘main’: logging.basicConfig(level=‘INFO’)

training_data_file = './data/stories.md'
model_path = './models/dialogue'

featurizer = MaxHistoryTrackerFeaturizer(BinarySingleStateFeaturizer(), max_history=5)
agent = Agent('restaurant_domain.yml', policies = [MemoizationPolicy(max_history = 4), KerasPolicy(featurizer)])

agent.train(
		training_data_file,
		augmentation_factor = 50,
		#max_history = 4,
		epochs = 500,
		batch_size = 30,
		validation_split = 0.2)
		
agent.persist(model_path)

Regards, ram