Can we run legacy python 2.7 code under python 3.5?

Question

I'd like to upgrade to python 3.5, but I use legacy python 2.7 packages. Is it easy to run legacy packages in python 3.5? I have been under the impression that this isn't easy, but I did a few searches to see if I'm wrong and didn't come up with much.

I would expect there to be a multiprocessing package that allows standardized hand-offs between 3.5 code and 2.7 packages, allowing them to run independently under their own environments, but being somewhat seamless to the developer.

I'm not talking about converting my own code to 3.5, I'm talking about libraries that I use that won't be updated for or by me.

Answer 1

If you used the newer syntax supported by 2.7, eg around exceptions, and/or, better yet, worked with new features imported from __future__ , you'll have much easier time converting your code to Python 3 (up to no changes at all). I'd suggest to follow this path first, for it can be trod gradually, without an abrupt jump to Python 3.

I suppose Python processes with different versions can interoperate, because object pickling format is compatible, and you can explicitly use a specific pickling protocol version on both sides to ensure that. I don't think multiprocessing packages on either side would be too useful, though. Consider using eg ZeroMQ as a more general solution.

Answer 2

Unfortunately there is no "nice" or automatic way of handling the processing of 2.7 code under 3.5 (that works perfectly).

You mentioned that you are concerned about libraries, not your own code - firstly, you'd hope that if they are under active development, they will be updated. If not, as you stated, then there is a possibility that they were written to be future proof. I've found some good ones are (eg google-api-python-client, eg https://github.com/google/google-api-python-client/blob/master/setup.py ).

Failing that, the only way to upgrade is to fix all the syntax changes yourself. Most common ones I deal with are around 'print' and exception handling.