This guide gets you started with gRPC in Python with a simple working example.

Before you begin

Prerequisites

Ensure you have pip version 8 or higher:

$ python -m pip install --upgrade pip

If you cannot upgrade pip due to a system-owned installation, you can run the example in a virtualenv:

$ python -m pip install virtualenv
$ virtualenv venv
$ source venv/bin/activate
$ python -m pip install --upgrade pip

Install gRPC

Install gRPC:

$ python -m pip install grpcio

Or, to install it system wide:

$ sudo python -m pip install grpcio

On El Capitan OSX, you may get the following error:

$ OSError: [Errno 1] Operation not permitted: '/tmp/pip-qwTLbI-uninstall/System/Library/Frameworks/Python.framework/Versions/2.7/Extras/lib/python/six-1.4.1-py2.7.egg-info'

You can work around this using:

$ python -m pip install grpcio --ignore-installed

Install gRPC tools

Python’s gRPC tools include the protocol buffer compiler protoc and the special plugin for generating server and client code from .proto service definitions. For the first part of our quickstart example, we’ve already generated the server and client stubs from helloworld.proto, but you’ll need the tools for the rest of our quickstart, as well as later tutorials and your own projects.

To install gRPC tools, run:

$ python -m pip install grpcio-tools

Download the example

You’ll need a local copy of the example code to work through this quickstart. Download the example code from our Github repository (the following command clones the entire repository, but you just need the examples for this quickstart and other tutorials):

$ # Clone the repository to get the example code:
$ git clone -b v1.4.x https://github.com/grpc/grpc
$ # Navigate to the "hello, world" Python example:
$ cd grpc/examples/python/helloworld

Run a gRPC application

From the examples/python/helloworld directory:

  1. Run the server

    $ python greeter_server.py
    
  2. In another terminal, run the client

    $ python greeter_client.py
    

Congratulations! You’ve just run a client-server application with gRPC.

Update a gRPC service

Now let’s look at how to update the application with an extra method on the server for the client to call. Our gRPC service is defined using protocol buffers; you can find out lots more about how to define a service in a .proto file in What is gRPC? and gRPC Basics: Python. For now all you need to know is that both the server and the client “stub” have a SayHello RPC method that takes a HelloRequest parameter from the client and returns a HelloResponse from the server, and that this method is defined like this:

// 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;
}

Let’s update this so that the Greeter service has two methods. Edit examples/protos/helloworld.proto and update it with a new SayHelloAgain method, with the same request and response types:

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

(Don’t forget to save the file!)

Generate gRPC code

Next we need to update the gRPC code used by our application to use the new service definition.

From the examples/python/helloworld directory, run:

$ python -m grpc_tools.protoc -I../../protos --python_out=. --grpc_python_out=. ../../protos/helloworld.proto

This regenerates helloworld_pb2.py which contains our generated request and response classes and helloworld_pb2_grpc.py which contains our generated client and server classes.

Update and run the application

We now have new generated server and client code, but we still need to implement and call the new method in the human-written parts of our example application.

Update the server

In the same directory, open greeter_server.py. Implement the new method like this:

class Greeter(helloworld_pb2_grpc.GreeterServicer):

  def SayHello(self, request, context):
    return helloworld_pb2.HelloReply(message='Hello, %s!' % request.name)

  def SayHelloAgain(self, request, context):
    return helloworld_pb2.HelloReply(message='Hello again, %s!' % request.name)
...

Update the client

In the same directory, open greeter_client.py. Call the new method like this:

def run():
  channel = grpc.insecure_channel('localhost:50051')
  stub = helloworld_pb2_grpc.GreeterStub(channel)
  response = stub.SayHello(helloworld_pb2.HelloRequest(name='you'))
  print("Greeter client received: " + response.message)
  response = stub.SayHelloAgain(helloworld_pb2.HelloRequest(name='you'))
  print("Greeter client received: " + response.message)

Run!

Just like we did before, from the examples/python/helloworld directory:

  1. Run the server

    $ python greeter_server.py
    
  2. In another terminal, run the client

    $ python greeter_client.py
    

What’s next