grpc/python/helloworld/README.md

gRPC Python Hello World

This is a quick introduction with a simple example and installation instructions: for a more complete tutorial see gRPC Basics: Python.

Install gRPC

Make sure you have built gRPC Python from source on your system. Follow the instructions here: https://github.com/grpc/grpc/blob/master/src/python/README.md.

This gives you a python virtual environment with installed gRPC Python in GRPC_ROOT/python2.7_virtual_environment. GRPC_ROOT is the path to which you have cloned the gRPC git repo.

Get the source code

The example code for our Hello World and our other examples live in the grpc-common GitHub repository. Clone this repository to your local machine by running the following command:

$ git clone https://github.com/grpc/grpc-common.git

Change your current directory to grpc-common/python/helloworld

$ cd grpc-common/python/helloworld/

Defining a service

The first step in creating our example is to define a service: an RPC service specifies the methods that can be called remotely with their parameters and return types. As you saw in the overview above, gRPC does this using protocol buffers. We use the protocol buffers interface definition language (IDL) to define our service methods, and define the parameters and return types as protocol buffer message types. Both the client and the server use interface code generated from the service definition.

Here's our example service definition, defined using protocol buffers IDL in helloworld.proto. The Greeting service has one method, hello, that lets the server receive a single HelloRequest message from the remote client containing the user's name, then send back a greeting in a single HelloReply. This is the simplest type of RPC you can specify in gRPC.

syntax = "proto3";

option java_package = "io.grpc.examples";

package helloworld;

// The greeting service definition.
service Greeter {
  // Sends a greeting
  rpc SayHello (HelloRequest) returns (HelloReply) {}
}

// The request message containing the user's name.
message HelloRequest {
  string name = 1;
}

// The response message containing the greetings
message HelloReply {
  string message = 1;
}

Generating gRPC code

Once we've defined our service, we use the protocol buffer compiler protoc to generate the special client and server code we need to create our application. The generated code contains both stub code for clients to use and an abstract interface for servers to implement, both with the method defined in our Greeting service.

To generate the client and server side interfaces:

$ ./run_codegen.sh

Which internally invokes the proto-compiler as:

$ protoc -I ../../protos --python_out=. --grpc_out=. --plugin=protoc-gen-grpc=`which grpc_python_plugin` ../../protos/helloworld.proto

Optionally, you can just skip the code generation step as the generated python module has already been generated for you (helloworld_pb2.py).

The client

Client-side code can be found in greeter_client.py.

You can run the client using:

$ ./run_client.sh

The server

Server side code can be found in greeter_server.py.

You can run the server using:

$ ./run_server.sh