You want to call a method in another process, potentially on another machine. In order to do that you both need to agree on what the networking protocol looks like. gRPC uses HTTP/2 for the control and data channel and uses Protocol Buffers to describe the method call, its parameters and ultimately its return values. Since this is standardized across languages it doesn't matter if the caller is Python and the callee is Java, you can still make the method call.
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You want to call a method in another process, potentially on another machine. In order to do that you both need to agree on what the networking protocol looks like. gRPC uses HTTP/2 for the control and data channel and uses Protocol Buffers to describe the method call, its parameters and ultimately its return values. Since this is standardized across languages it doesn't matter if the caller is Python and the callee is Java, you can still make the method call.