erlang interface to python

I've been expanding on python version of Armstrong's classical example of interfaces. Everything works fine while I communicate bytes. But, I'd like to communicate long integers and floats. Mabye even (oh, no) strings. Here is my code: http://pastebin.com/epxgDmvu http://pastebin.com/rD7CWRkz

First of all, all that I know how to send are bytes. Can erlang send anything else to it's inteface? Or do I have to convert float to list of bytes, send it to python and then assemble it back to float in python?

And, the ohter way around: if I pack with 'f' format, erlang recognises that as a list of bytes. Is there a way to persuade erlang to take those bytes as one single float? If not, where can I find out how to convert that erlang list to erlang float?

In case erlang can communicate only bytes, how do you propose that I send a list of integers? If I convert integers to lists of bytes, then I can't send them in one message since reciever won't know where one integer ends and other begins, right? Should I then send integers one by one?

Yes, I am looking into ErlPort and py-interface and some other, but I'd like to start from fundamentals.

Regards, dijxtra

At a low (from programming point of view) level you always send/receive only a bunch of bytes through different external interfaces (pipes, network, files...) independently from a programming language you're using. For example when you work with pipes (which you got calling open_port/2) you send/receive data as a stream of bytes.

To send any useful information through a stream you need to divide it to chunks which usually named messages. Message format define how messages can be extracted from a stream of bytes. For example using Type-Length-Value (TLV) encoding you can send values of different length marked with a type.

In ErlPort it all works as following:

When you call open_port/2 you must add option {packet, N} so all binary messages sent through this port are preceded by their length, sent in N bytes (Length-Value encoding).
Before to send a term to the port you must use term_to_binary/1 function which encode Erlang term to a bunch of bytes using Erlang external term format.
On Python side when you instantiate erlproto.Port class you must pass the same packet value as you pass to open_port/2 (packet=1 by default).
Port.read method first read the length of the message from the stream and then the message body.
The message body decoded by the erlterms.decode function.
When you send a reply using Port.write method it's first encoded to Erlang external term format by erlterms.encode function.
Then the encoded chunk prepended by its length sent back to Erlang.
On Erlang side binary_to_term/1 is used to decode the data.