title: Python grpc protobuf stubs generation issue: --grpc_out: protoc-gen-grpc: Plugin failed with status code 1
body: <p>As the question says, I compiled grpc from source and also did <code>sudo pip install grpcio</code>, however, the <code>which grpc_python_plugin</code> doesn't return anything. This is a problem because the grpc python example for route_guide requires me to run <code>protoc -I . --python_out=. --grpc_out=. --plugin=protoc-gen-grpc='which grpc_python_plugin' ./route_guide.proto</code>
   in order to generate the python stubs. Since, <code>which grpc_python_plugin</code> doesn't return anything, I get the following error:</p>
  
  <pre><code>: program not found or is not executable
  --grpc_out: protoc-gen-grpc: Plugin failed with status code 1.
  </code></pre>
  
  <p>If I shorten the command I'm trying to run to:<code>protoc -I . --python_out=. ./route_guide.proto</code>, it generates the route_guide_pb2.py file but without the Servicer and Stub classes, and server and stub methods. Ofc, these methods are necessary if one wants to use grpc for any purpose. Any help would be appreciated.</p>