diff --git a/.gitignore b/.gitignore
index d697b92..8ee6691 100644
--- a/.gitignore
+++ b/.gitignore
@@ -4,8 +4,8 @@ leela-zero
 parameters
 *.swp
 *.sublime*
-checkpoints
-checkpoints_origin
+checkpoint
 *.json
 .DS_Store
 data
+.log
diff --git a/AlphaGo/game.py b/AlphaGo/game.py
index ff1faf5..90d0bf0 100644
--- a/AlphaGo/game.py
+++ b/AlphaGo/game.py
@@ -27,29 +27,30 @@ class Game:
     '''
     def __init__(self, name="go", checkpoint_path=None):
         self.name = name
-        if "go" == name:
+        if self.name == "go":
             self.size = 9
             self.komi = 3.75
             self.board = [utils.EMPTY] * (self.size ** 2)
             self.history = []
+            self.history_length = 8
             self.latest_boards = deque(maxlen=8)
             for _ in range(8):
                 self.latest_boards.append(self.board)
-
-            self.evaluator = model.ResNet(self.size, self.size**2 + 1, history_length=8)
             self.game_engine = go.Go(size=self.size, komi=self.komi)
-        elif "reversi" == name:
+        elif self.name == "reversi":
             self.size = 8
-            self.evaluator = model.ResNet(self.size, self.size**2 + 1, history_length=1)
+            self.history_length = 1
             self.game_engine = reversi.Reversi()
             self.board = self.game_engine.get_board()
         else:
-            print(name + " is an unknown game...")
+            raise ValueError(name + " is an unknown game...")
+
+        self.evaluator = model.ResNet(self.size, self.size ** 2 + 1, history_length=self.history_length)
 
     def clear(self):
         self.board = [utils.EMPTY] * (self.size ** 2)
         self.history = []
-        for _ in range(8):
+        for _ in range(self.history_length):
             self.latest_boards.append(self.board)
 
     def set_size(self, n):
@@ -76,9 +77,9 @@ class Game:
         if vertex == utils.PASS:
             return True
         # TODO this implementation is not very elegant
-        if "go" == self.name:
+        if self.name == "go":
             res = self.game_engine.executor_do_move(self.history, self.latest_boards, self.board, color, vertex)
-        elif "revsersi" == self.name:
+        elif self.name == "reversi":
             res = self.game_engine.executor_do_move(self.board, color, vertex)
         return res
 
diff --git a/AlphaGo/player.py b/AlphaGo/player.py
index 0e3daff..e848d2b 100644
--- a/AlphaGo/player.py
+++ b/AlphaGo/player.py
@@ -34,7 +34,7 @@ if __name__ == '__main__':
 
     daemon = Pyro4.Daemon()                # make a Pyro daemon
     ns = Pyro4.locateNS()                  # find the name server
-    player = Player(role = args.role, engine = engine)
+    player = Player(role=args.role, engine=engine)
     print "Init " + args.role + " player finished"
     uri = daemon.register(player)          # register the greeting maker as a Pyro object
     print "Start on name " + args.role
diff --git a/README.md b/README.md
index 9c3af16..fc7d494 100644
--- a/README.md
+++ b/README.md
@@ -41,6 +41,11 @@ Tianshou(天授) is a reinforcement learning platform. The following image illus
 
 <img src="https://github.com/sproblvem/tianshou/blob/master/docs/figures/go.png" height="150"/> <img src="https://github.com/sproblvem/tianshou/blob/master/docs/figures/reversi.jpg" height="150"/> <img src="https://github.com/sproblvem/tianshou/blob/master/docs/figures/warzone.jpg" height="150"/>
 
+## examples
+
+During development, run examples under `./examples/` directory with, e.g. `python ppo_example.py`.
+Running them under this directory with `python examples/ppo_example.py` will not work.
+
 
 ## About coding style
 
diff --git a/examples/ppo_example.py b/examples/ppo_example.py
index 02ccb52..985c8f2 100755
--- a/examples/ppo_example.py
+++ b/examples/ppo_example.py
@@ -1,17 +1,16 @@
 #!/usr/bin/env python
+from __future__ import absolute_import
 
 import tensorflow as tf
-import numpy as np
-import time
 import gym
 
 # our lib imports here!
 import sys
 sys.path.append('..')
-import tianshou.core.losses as losses
+from tianshou.core import losses
 from tianshou.data.batch import Batch
 import tianshou.data.advantage_estimation as advantage_estimation
-import tianshou.core.policy as policy
+import tianshou.core.policy.stochastic as policy  # TODO: fix imports as zhusuan so that only need to import to policy
 
 
 def policy_net(observation, action_dim, scope=None):
diff --git a/tianshou/core/policy/__init__.py b/tianshou/core/policy/__init__.py
index ccde775..e69de29 100644
--- a/tianshou/core/policy/__init__.py
+++ b/tianshou/core/policy/__init__.py
@@ -1,6 +0,0 @@
-#!/usr/bin/env python
-# -*- coding: utf-8 -*-
-
-from .base import *
-from .stochastic import *
-from .dqn import *
\ No newline at end of file
diff --git a/tianshou/core/policy/base.py b/tianshou/core/policy/base.py
index 025abd5..1adeaeb 100644
--- a/tianshou/core/policy/base.py
+++ b/tianshou/core/policy/base.py
@@ -13,11 +13,23 @@ import tensorflow as tf
 __all__ = [
     'StochasticPolicy',
     'QValuePolicy',
+    'PolicyBase'
 ]
 
 # TODO: a even more "base" class for policy
 
 
+class PolicyBase(object):
+    """
+    base class for policy. only provides `act` method with exploration
+    """
+    def __init__(self):
+        pass
+
+    def act(self, observation, exploration):
+        raise NotImplementedError()
+
+
 class QValuePolicy(object):
     """
     The policy as in DQN
diff --git a/tianshou/core/policy/dqn.py b/tianshou/core/policy/dqn.py
index d03dbd4..716e4c4 100644
--- a/tianshou/core/policy/dqn.py
+++ b/tianshou/core/policy/dqn.py
@@ -1,16 +1,22 @@
-from tianshou.core.policy.base import QValuePolicy
+from __future__ import absolute_import
+
+from .base import PolicyBase
 import tensorflow as tf
-import sys
-sys.path.append('..')
-import value_function.action_value as value_func
+from ..value_function.action_value import DQN
 
 
-class DQN_refactor(object):
+class DQNRefactor(PolicyBase):
     """
     use DQN from value_function as a member
     """
     def __init__(self, value_tensor, observation_placeholder, action_placeholder):
-        self._network = value_func.DQN(value_tensor, observation_placeholder, action_placeholder)
+        self._network = DQN(value_tensor, observation_placeholder, action_placeholder)
+        self._argmax_action = tf.argmax(value_tensor, axis=1)
+
+    def act(self, observation, exploration):
+        sess = tf.get_default_session()
+        if not exploration:  # no exploration
+             action = sess.run(self._argmax_action, feed_dict={})
 
 
 class DQN(QValuePolicy):
diff --git a/tianshou/core/value_function/action_value.py b/tianshou/core/value_function/action_value.py
index cb8acc8..2bda4fa 100644
--- a/tianshou/core/value_function/action_value.py
+++ b/tianshou/core/value_function/action_value.py
@@ -1,4 +1,6 @@
-from base import ValueFunctionBase
+from __future__ import absolute_import
+
+from .base import ValueFunctionBase
 import tensorflow as tf
 
 
@@ -15,7 +17,6 @@ class ActionValue(ValueFunctionBase):
 
     def get_value(self, observation, action):
         """
-
         :param observation: numpy array of observations, of shape (batchsize, observation_dim).
         :param action: numpy array of actions, of shape (batchsize, action_dim)
         # TODO: Atari discrete action should have dim 1. Super Mario may should have, say, dim 5, where each can be 0/1
@@ -24,7 +25,7 @@ class ActionValue(ValueFunctionBase):
         """
         sess = tf.get_default_session()
         return sess.run(self.get_value_tensor(), feed_dict=
-        {self._observation_placeholder: observation, self._action_placeholder:action})[:, 0]
+        {self._observation_placeholder: observation, self._action_placeholder: action})
 
 
 class DQN(ActionValue):
@@ -39,13 +40,21 @@ class DQN(ActionValue):
         :param action_placeholder: of shape (batchsize, )
         """
         self._value_tensor_all_actions = value_tensor
-        canonical_value_tensor = value_tensor[action_placeholder]  # maybe a tf.map_fn. for now it's wrong
+
+        batch_size = tf.shape(value_tensor)[0]
+        batch_dim_index = tf.range(batch_size)
+        indices = tf.stack([batch_dim_index, action_placeholder], axis=1)
+        canonical_value_tensor = tf.gather_nd(value_tensor, indices)
 
         super(DQN, self).__init__(value_tensor=canonical_value_tensor,
                                   observation_placeholder=observation_placeholder,
                                   action_placeholder=action_placeholder)
 
     def get_value_all_actions(self, observation):
+        """
+        :param observation:
+        :return: numpy array of Q(s, *) given s, of shape (batchsize, num_actions)
+        """
         sess = tf.get_default_session()
         return sess.run(self._value_tensor_all_actions, feed_dict={self._observation_placeholder: observation})
 
diff --git a/tianshou/core/value_function/base.py b/tianshou/core/value_function/base.py
index 0b27759..b15f1bf 100644
--- a/tianshou/core/value_function/base.py
+++ b/tianshou/core/value_function/base.py
@@ -1,3 +1,6 @@
+from __future__ import absolute_import
+
+import tensorflow as tf
 
 # TODO: linear feature baseline also in tf?
 class ValueFunctionBase(object):
@@ -6,7 +9,7 @@ class ValueFunctionBase(object):
     """
     def __init__(self, value_tensor, observation_placeholder):
         self._observation_placeholder = observation_placeholder
-        self._value_tensor = value_tensor
+        self._value_tensor = tf.squeeze(value_tensor)  # canonical values has shape (batchsize, )
 
     def get_value(self, **kwargs):
         """
diff --git a/tianshou/core/value_function/state_value.py b/tianshou/core/value_function/state_value.py
index 04fe442..b7de196 100644
--- a/tianshou/core/value_function/state_value.py
+++ b/tianshou/core/value_function/state_value.py
@@ -1,4 +1,6 @@
-from base import ValueFunctionBase
+from __future__ import absolute_import
+
+from .base import ValueFunctionBase
 import tensorflow as tf
 
 
@@ -17,7 +19,7 @@ class StateValue(ValueFunctionBase):
 
         :param observation: numpy array of observations, of shape (batchsize, observation_dim).
         :return: numpy array of state values, of shape (batchsize, )
-        # TODO: dealing with the last dim of 1 in V(s) and Q(s, a)
+        # TODO: dealing with the last dim of 1 in V(s) and Q(s, a), this should rely on the action shape returned by env
         """
         sess = tf.get_default_session()
-        return sess.run(self.get_value_tensor(), feed_dict={self._observation_placeholder: observation})[:, 0]
\ No newline at end of file
+        return sess.run(self.get_value_tensor(), feed_dict={self._observation_placeholder: observation})
\ No newline at end of file