The March To 3

The How's and Why's of porting to Python 3.

1. The March To3
2. Who? • Daniel Lindsley • Pythonista since 2003 • Djangonaut since 2006 • Author of Tastypie / Haystack / itty / others
4. Your language is...
5. Your language is... DEAD
6. Your language is... DEAD ...for small values of “dead”.
9. ⦸
12. ⦸
14. is dead;
15. is dead; Long live !
17. Why port to Python 3?
18. Active Development Python 2.7.x will only get security updates. No Python 2.8 ever.
19. As Fast As 2.7 With 3.3 & it’ll only get better.
20. Cleaned Up Syntax We’ll get to some of these in a bit.
21. Better String Handling Unicode everywhere.
22. Stable
24. Changes from 2 to 3 •Removals • Backticks, classic classes • <>, apply, reduce, dict.has_key • Others
25. Changes from 2 to 3 •Changed • print is now print() • next() is now __next__() • Better raise syntax • Metaclasses
26. Changes from 2 to 3 •Changed (cont.) • Faster Decimal implementation • Reorganized & spruced up stdlib • Careful with I/O!
27. Changes from 2 to 3 •New! • Built-in OrderedDict • String formatting • dict / set comprehensions • Generator delegation via yield from
28. Changes from 2 to 3 •New! (cont.) • Built-in virtualenv support! • unittest2 by default! • World domination with importlib
30. “What versions should I support?”
31. “What versions should I support?” Simple answer: Python 2.6+ & Python 3.3+
33. “So how do I port?”
34. IT DEPENDS!
35. Decide between... • A One-time port • A Combined 2 & 3 codebase ...or...
37. The One-time port
38. The One-time port • Ensure you have good test coverage • Use 2to3 to convert the codebase • Run tests & fix until it passes
40. The Combined 2 & 3 codebase
41. The Combined 2 & 3 codebase • First, you need a venv: •virtualenv -p python3 env3 •. env3/bin/activate
42. The Combined 2 & 3 codebase • Ensure you have good test coverage • Require six as a dependency • Use six to patch over the differences • Run tests in Py3 & fix until it passes... • ...then run tests in Py2 & fix until it passes!
44. Using six in practice
45. Demo time.
47. More information • http://pyvideo.org/video/1730/python-33- trust-me-its-better-than-27 • http://pyvideo.org/video/1787/porting- django-apps-to-python-3 • http://pyvideo.org/video/1704/why-you- should-use-python-3-for-text-processing • http://pythonhosted.org/six/
48. More information • http://www.dabeaz.com/python3io/ MasteringIO.pdf
49. Thanks! @daniellindsley https://github.com/toastdriven