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

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“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.” — https://docs.djangoproject.com/en/1.5/releases/1.5/

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Do I want to use Python 3?

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ˑYes!

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Python 3: now with 30% fewer warts!

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ˑ Unicode no longer sucks!

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Can I use Python 3?

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✓ SQLite ✓ PostgreSQL ✘ MySQL

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✓ modwsgi ✓ uWSGI ✓ gunicorn: sync ✘ gunicorn: async

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✓ South ✓ Celery ✓ django-pipeline ✘ django-debug-toolbar ✘ django-registration ✘ django-extensions ✘ Haystack ✘ django-tagging ✘ Sentry ✘ django-compressor

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Should I use Python 3?

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

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Python 3 only?

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2to3

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ˑ Single source wins!

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HOWTO

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1. Choose an approach

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2. Evaluate dependencies

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3. Get the test suite running

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4. Fix unicode handling

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5. Iterate on test failures

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Case study: a new website

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

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2. Evaluate dependencies • Light CMS capabilities. • Moderately complex user / permissions / authentication system. • Heavy integration with social networks. • Moderate traffic with extreme “spikes.”

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

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4. Fix unicode handling django.utils.encoding

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ˑIt works! ... but costs ~20% more.

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

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1. Choose an approach Shared source: Python 2.6+, 3.3; Django 1.4+

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2. Evaluate dependencies None (whew).

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

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Tox [tox] envlist  -­‐  py27-­‐django14,  py33-­‐django15 [py27-­‐django14] basepython  =  python2.7 deps  =  Django==1.4 [py33-­‐django15] basepython  =  python33 deps  =  Django==1.5

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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

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4. Fix unicode handling django.utils.encoding

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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

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

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

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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

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Six if  six.PY3: ...

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ˑ django.me/py3 is your new bicycle

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Thanks! Jacob Kaplan-Moss [email protected] Questions? Follow me to room 201!