mpi-less ppo2 (resolving merge conflict)

baselines/ppo2/model.py

@@ -2,11 +2,15 @@ import tensorflow as tf
 import functools
 
 from baselines.common.tf_util import get_session, save_variables, load_variables
-from baselines.common.mpi_adam_optimizer import MpiAdamOptimizer
 from baselines.common.tf_util import initialize
-from baselines.common.mpi_util import sync_from_root
 
 from mpi4py import MPI
+try:
+    from baselines.common.mpi_adam_optimizer import MpiAdamOptimizer
+    from mpi4py import MPI
+    from baselines.common.mpi_util import sync_from_root
+except ImportError:
+    MPI = None
 
 class Model(object):
     """
@@ -88,7 +92,10 @@ class Model(object):
         # 1. Get the model parameters
         params = tf.trainable_variables('ppo2_model')
         # 2. Build our trainer
-        self.trainer = MpiAdamOptimizer(MPI.COMM_WORLD, learning_rate=LR, epsilon=1e-5)
+        if MPI is not None:
+            self.trainer = MpiAdamOptimizer(MPI.COMM_WORLD, learning_rate=LR, epsilon=1e-5)
+        else:
+            self.trainer = tf.train.AdamOptimizer(learning_rate=LR, epsilon=1e-5)
         # 3. Calculate the gradients
         grads_and_var = self.trainer.compute_gradients(loss, params)
         grads, var = zip(*grads_and_var)
@@ -116,7 +123,7 @@ class Model(object):
         self.save = functools.partial(save_variables, sess=sess)
         self.load = functools.partial(load_variables, sess=sess)
 
-        if MPI.COMM_WORLD.Get_rank() == 0:
+        if MPI is None or MPI.COMM_WORLD.Get_rank() == 0:
             initialize()
         global_variables = tf.get_collection(tf.GraphKeys.GLOBAL_VARIABLES, scope="")
         sync_from_root(sess, global_variables) #pylint: disable=E1101