diff --git a/examples/actor_critic.py b/examples/actor_critic.py
index 97825b9..2e3a8a5 100755
--- a/examples/actor_critic.py
+++ b/examples/actor_critic.py
@@ -7,16 +7,6 @@ import gym
 
 import tianshou as ts
 
-import sys
-sys.path.append('..')
-from tianshou.core import losses
-import tianshou.data.advantage_estimation as advantage_estimation
-import tianshou.core.policy.distributional as policy
-import tianshou.core.value_function.state_value as value_function
-
-from tianshou.data.data_buffer.batch_set import BatchSet
-from tianshou.data.data_collector import DataCollector
-
 
 if __name__ == '__main__':
     env = gym.make('CartPole-v0')
diff --git a/examples/ddpg.py b/examples/ddpg.py
index 9579129..17a67a7 100644
--- a/examples/ddpg.py
+++ b/examples/ddpg.py
@@ -9,20 +9,6 @@ import argparse
 
 import tianshou as ts
 
-# our lib imports here! It's ok to append path in examples
-import sys
-sys.path.append('..')
-from tianshou.core import losses
-import tianshou.data.advantage_estimation as advantage_estimation
-import tianshou.core.policy as policy
-import tianshou.core.value_function.action_value as value_function
-import tianshou.core.opt as opt
-
-from tianshou.data.data_buffer.vanilla import VanillaReplayBuffer
-from tianshou.data.data_collector import DataCollector
-from tianshou.data.tester import test_policy_in_env
-from tianshou.core.utils import get_soft_update_op
-
 
 if __name__ == '__main__':
     parser = argparse.ArgumentParser()
diff --git a/tianshou/core/policy/deterministic.py b/tianshou/core/policy/deterministic.py
index 5ea3683..a1cd4da 100644
--- a/tianshou/core/policy/deterministic.py
+++ b/tianshou/core/policy/deterministic.py
@@ -146,7 +146,8 @@ class Deterministic(PolicyBase):
         """
         sess = tf.get_default_session()
 
-        feed_dict = {self.observation_placeholder: observation}.update(my_feed_dict)
+        feed_dict = {self.observation_placeholder: observation}
+        feed_dict.update(my_feed_dict)
         action = sess.run(self.action, feed_dict=feed_dict)
 
         return action
@@ -164,7 +165,8 @@ class Deterministic(PolicyBase):
         """
         sess = tf.get_default_session()
 
-        feed_dict = {self.observation_placeholder: observation}.update(my_feed_dict)
+        feed_dict = {self.observation_placeholder: observation}
+        feed_dict.update(my_feed_dict)
         action = sess.run(self.action_old, feed_dict=feed_dict)
 
         return action
\ No newline at end of file
diff --git a/tianshou/core/value_function/action_value.py b/tianshou/core/value_function/action_value.py
index 599b1da..56ae1d3 100644
--- a/tianshou/core/value_function/action_value.py
+++ b/tianshou/core/value_function/action_value.py
@@ -80,8 +80,9 @@ class ActionValue(ValueFunctionBase):
         :return: A numpy array of shape (batch_size,). The corresponding action value for each observation.
         """
         sess = tf.get_default_session()
-        return sess.run(self.value_tensor, feed_dict=
-        {self.observation_placeholder: observation, self.action_placeholder: action}.update(my_feed_dict))
+        feed_dict = {self.observation_placeholder: observation, self.action_placeholder: action}
+        feed_dict.update(my_feed_dict)
+        return sess.run(self.value_tensor, feed_dict=feed_dict)
 
     def eval_value_old(self, observation, action, my_feed_dict={}):
         """
@@ -95,7 +96,8 @@ class ActionValue(ValueFunctionBase):
         :return: A numpy array of shape (batch_size,). The corresponding action value for each observation.
         """
         sess = tf.get_default_session()
-        feed_dict = {self.observation_placeholder: observation, self.action_placeholder: action}.update(my_feed_dict)
+        feed_dict = {self.observation_placeholder: observation, self.action_placeholder: action}
+        feed_dict.update(my_feed_dict)
         return sess.run(self.value_tensor_old, feed_dict=feed_dict)
 
     def sync_weights(self):
@@ -198,7 +200,8 @@ class DQN(ValueFunctionBase):
         :return: A numpy array of shape (batch_size,). The corresponding action value for each observation.
         """
         sess = tf.get_default_session()
-        feed_dict = {self.observation_placeholder: observation, self.action_placeholder: action}.update(my_feed_dict)
+        feed_dict = {self.observation_placeholder: observation, self.action_placeholder: action}
+        feed_dict.update(my_feed_dict)
         return sess.run(self.value_tensor, feed_dict=feed_dict)
 
     def eval_value_old(self, observation, action, my_feed_dict={}):
@@ -213,7 +216,8 @@ class DQN(ValueFunctionBase):
         :return: A numpy array of shape (batch_size,). The corresponding action value for each observation.
         """
         sess = tf.get_default_session()
-        feed_dict = {self.observation_placeholder: observation, self.action_placeholder: action}.update(my_feed_dict)
+        feed_dict = {self.observation_placeholder: observation, self.action_placeholder: action}
+        feed_dict.update(my_feed_dict)
         return sess.run(self.value_tensor_old, feed_dict=feed_dict)
 
     @property
@@ -232,7 +236,9 @@ class DQN(ValueFunctionBase):
         :return: A numpy array of shape (batch_size, num_actions). The corresponding action values for each observation.
         """
         sess = tf.get_default_session()
-        return sess.run(self._value_tensor_all_actions, feed_dict={self.observation_placeholder: observation}.update(my_feed_dict))
+        feed_dict = {self.observation_placeholder: observation}
+        feed_dict.update(my_feed_dict)
+        return sess.run(self._value_tensor_all_actions, feed_dict=feed_dict)
 
     def eval_value_all_actions_old(self, observation, my_feed_dict={}):
         """
@@ -245,7 +251,9 @@ class DQN(ValueFunctionBase):
         :return: A numpy array of shape (batch_size, num_actions). The corresponding action values for each observation.
         """
         sess = tf.get_default_session()
-        return sess.run(self.value_tensor_all_actions_old, feed_dict={self.observation_placeholder: observation}.update(my_feed_dict))
+        feed_dict = {self.observation_placeholder: observation}
+        feed_dict.update(my_feed_dict)
+        return sess.run(self.value_tensor_all_actions_old, feed_dict=feed_dict)
 
     def sync_weights(self):
         """
diff --git a/tianshou/core/value_function/state_value.py b/tianshou/core/value_function/state_value.py
index 76da7b2..7d43a28 100644
--- a/tianshou/core/value_function/state_value.py
+++ b/tianshou/core/value_function/state_value.py
@@ -79,7 +79,9 @@ class StateValue(ValueFunctionBase):
         :return: A numpy array of shape (batch_size,). The corresponding state value for each observation.
         """
         sess = tf.get_default_session()
-        return sess.run(self.value_tensor, feed_dict={self.observation_placeholder: observation}.update(my_feed_dict))
+        feed_dict = {self.observation_placeholder: observation}
+        feed_dict.update(my_feed_dict)
+        return sess.run(self.value_tensor, feed_dict=feed_dict)
 
     def eval_value_old(self, observation, my_feed_dict={}):
         """
@@ -92,7 +94,9 @@ class StateValue(ValueFunctionBase):
         :return: A numpy array of shape (batch_size,). The corresponding state value for each observation.
         """
         sess = tf.get_default_session()
-        return sess.run(self.value_tensor_old, feed_dict={self.observation_placeholder: observation}.update(my_feed_dict))
+        feed_dict = {self.observation_placeholder: observation}
+        feed_dict.update(my_feed_dict)
+        return sess.run(self.value_tensor_old, feed_dict=feed_dict)
 
     def sync_weights(self):
         """