Python 3 Universally


A Python user is starting a project and thinks to themselves, “Yay, new code! I can use Python 3 for this!”. They install the latest Anaconda for Py3 and get to work. A few days and hundreds of lines of code later they find out that a particular library they need (maybe imposm.parser) only supports Python 2. Our well intentioned user sighs, re-installs Anaconda for Py2, and carries on. Maybe next time (or maybe not). (This is a semi-autobiographical story.)

Elsewhere, a Python library maintainer is excited about Py3’s new asyncio module and could put it to immediate use but doesn’t want to alienate users who are stuck on Py2.

There are many valid reasons to be using Py2 today: a dated dependency, the inertia of existing code, not wanting to break a working setup, not knowing how/why to switch, and lack of time.

There are also many valid reasons for wanting to develop exclusively for Py3: access to new features, reduced support burden, simplified maintenance, wanting to get ahead of the 2020 end-of-support for Py2, and lack of time. These tensions have the potential to create much frustration in the Python community, but I think with some intentional effort on the part of Python developers and leaders it will all be fine. Read More »

C Extensions for Python 2 and 3

One of my upcoming tasks at work is converting Pandana to support both Python 2 and 3. The tricky bit is that Pandana has a C extension written in plain C using the Python 2 C-API, which is not compatible with Python 3.

It seems like the best way to have a C extension that supports both Python 2 and 3 is to not write the extension in C. These days there are a number of alternatives that allow you to write interfaces in Python or something like Python (Cython). I decided to make a sample project with some C functions to wrap so that I could try out CFFI, Cython, and the standard library ctypes module.

You can find the project with examples of all three and a longer writeup at Pull requests are welcome on the repo with further examples!