--- a
+++ b/rdpg/history.py
@@ -0,0 +1,18 @@
+class History(object):
+	def __init__(self,init_state):
+		self.observations = [init_state]
+		self.actions = []
+		self.rewards = []
+	# append observation
+	def append_o(self,state):
+		self.observations.append(state)
+	# append action
+	def append_a(self,action):
+		self.actions.append(action)
+	# append reward
+	def append_r(self,reward):
+		self.rewards.append(reward)
+	def append(self,state,action,reward):
+		self.append_o(state)
+		self.append_a(action)
+		self.append_r(reward)