refine import path for ps_instance.py

test=develop

python/paddle/fluid/distributed/helper.py

@@ -12,7 +12,6 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from mpi4py import MPI
 import ps_pb2 as pslib
 
 
@@ -59,7 +58,7 @@ class FileSystem(object):
 
 class MPIHelper(object):
     """
-    MPIHelper is a wrapper of mpi4py, supprot get_rank get_size etc.
+    MPIHelper is a wrapper of mpi4py, support get_rank get_size etc.
     Args:
         No params
     Examples:
@@ -68,7 +67,9 @@ class MPIHelper(object):
     """
 
     def __init__(self):
+        from mpi4py import MPI
         self.comm = MPI.COMM_WORLD
+        self.MPI = MPI
 
     def get_rank(self):
         return self.comm.Get_rank()
@@ -86,4 +87,4 @@ class MPIHelper(object):
         return socket.gethostname()
 
     def finalize(self):
-        MPI.Finalize()
+        self.MPI.Finalize()

python/requirements.txt

@@ -9,4 +9,3 @@ Pillow
 nltk>=3.2.2
 graphviz
 six
-mpi4py==3.0.0