Porting Django apps to Python 3

Jacob Kaplan-Moss

July 04, 2013

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1. Porting Django apps to Python 3 Jacob Kaplan-Moss[email protected]

2. “Django 1.5 is… the first release with Python 3 support!

   ... Everything’s in place for you to start porting your apps to Python 3.” — http://django.me/1.5 “As of Django 1.6, Python 3 support is considered stable and you can safely use it in production. — http://django.me/faq

3. Do I want to use Python 3?

4. ˑYes!

5. Python 3: now with 30% fewer warts!

6. ˑ Unicode no longer sucks!

7. Can I use Python 3?

8. ✓ SQLite ✓ PostgreSQL ✘ MySQL* ? Oracle

9. ✓ modwsgi ✓ uWSGI ✓ gunicorn: sync ? gunicorn: async

10. ✓ South ✓ Celery ✓ Raven (Sentry) ✓ django-extensions ✘

    django-compressor ✘ django-social-auth ✘ django-tagging ✘ django-debug-toolbar ✘ django-registration ✘ Haystack

11. ✓ South ✓ Celery ✓ Raven (Sentry) ✓ django-extensions ✓

    django-pipeline ✓ django-allauth ✓ django-taggit ✘ django-debug-toolbar ✘ django-registration ✘ Haystack

12. Should I use Python 3?

13. Options 1. Python 3 only. 2. Translated source (2to3). 3.

    Single codebase.

14. Python 3 only?

15. 2to3

16. ˑ Single source wins!

17. HOWTO

18. 1. Choose an approach

19. 2. Evaluate dependencies

20. 3. Get the test suite running

21. 4. Fix unicode handling

22. 5. Iterate on test failures

23. Case study: a new website

24. 1. Choose an approach Single source: Python 3.3 only.

25. 2. Evaluate dependencies • Light CMS capabilities. • Moderately complex

    user / permissions / authentication system. • Heavy integration with social networks. • Moderate traffic with extreme “spikes.”

26. 3. Get the test suite running ✓ django-discover-runner

27. 4. Fix unicode handling django.utils.encoding

28. ˑIt works! ... but costs ~20% more.

29. Case study: django-sitetree Ported by Jeff Triplett (@webology) https://github.com/idlesign/django-sitetree/commit/c7475

30. 1. Choose an approach Shared source: Python 2.6+, 3.3; Django

    1.4+

31. 2. Evaluate dependencies None (whew).

32. 3. Get the test suite running Tox: http://tox.readthedocs.org/

33. Tox [tox] envlist  -­‐  py27-­‐django14,  py33-­‐django15 [py27-­‐django14] basepython  =  python2.7

    deps  =  Django==1.4 [py33-­‐django15] basepython  =  python33 deps  =  Django==1.5

34. Syntax changes print  "foo"   print("foo") except  Exception,  ex:  

    except  Exception  as  ex: raise  Exception,  "msg"        raise  Exception("message”) class  C:                                    class  C(metaclass=M)      __metaclass__  =  M More: http://docs.python.org/3.0/whatsnew/3.0.html 2 3

35. 4. Fix unicode handling django.utils.encoding

36. Models and unicode class  M(models.Model):   class  M(models.Model):    

       def  __unicode__(self):            def  __str__(self):                return  self.name                  return  self.name @python_2_unicode_compat class  M(models.Model):        def  __str__(self):                return  self.name 2 3

37. 5. Iterate on test failures Six: http://pythonhosted.org/six/ (also django.utils.six)

38. Six class  C:              

                         class  C(metaclass=M)      __metaclass__  =  M class  C(six.with_metaclass(M)): 2 3

39. Six isinstance(s,  str)   isinstance(s,  bytes) isinstance(s,  unicode)   isinstance(s,

     str) isinstance(s,  six.binary_type) isinstance(s,  six.text_type) 2 3

40. Six if  six.PY3: ...

41. More info: django.me/py3

42. ˑ We’ve done our job…

43. ˑ We’ve done our job… now it’s your turn!

44. Thanks! Jacob Kaplan-Moss[email protected]