The best (and worst) of Django

The best (and worst) of Django

Given at OSCON 2011.

2f5463832ccb768ccb4a1ca3607c27ef?s=128

Jacob Kaplan-Moss

March 22, 2012
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Transcript

  1. 2.
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  4. 9.

    The “application” is the whole site — no apps, no

    components, no modules. Makes heavy use of site-wide logic: middleware, context processors and custom plugin-like concepts. The monolith monster
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  6. 16.

    The Django mindset: Application: some bit of functionality. Site: several

    applications. Spin off new apps liberally. A suite of apps ready for use.
  7. 17.

             

                                                                                                                                                                                                 !                 !                         !      "                   #                   !           $        !                                                   "                     %          &   &                             '         !    (                                       )      *  +      !                                       %+ ,             &  - 
  8. 21.

    The Django mindset: A great and powerful respect for data.

    Model the data correctly and the rest of the site will just fall out of that. Denormalization is all well and good, but never throw data away.
  9. 24.

    class  BaseObject(models.Model):        creation_date  =  models.DateField()    

       … class  Animal(BaseObject):        … class  Vegetable(BaseObject):        … class  Mineral(BaseObject):        …
  10. 25.
  11. 28.

    Without a concrete base class: >>>  Animal.objects.all() SELECT  ...  FROM

     animal; With a concrete base class: >>>  Animal.objects.all()
  12. 29.

    Without a concrete base class: >>>  Animal.objects.all() SELECT  ...  FROM

     animal; With a concrete base class: >>>  Animal.objects.all() SELECT  ...  FROM  "animal"  INNER  JOIN  "baseobject"   ON  ("animal"."baseobject_ptr_id"  =  "baseobject"."id")
  13. 30.
  14. 32.

    What you want: >>>  BaseObject.objects.all() [<Animal:  Frog>,  <Vegetable:  Carrot>,  <Mineral:

     Gold>,  ...] What you get: >>>  BaseObject.objects.all() [<BaseObject:  1>,  <BaseObject:  2>,  <BaseObject:  3>,  ...]
  15. 33.

    So maybe you try something like: def  get_some_of_everything():    

       qs  =  BaseObject.objects.all()        for  obj  in  qs:                for  cls  in  BaseObject.__subclasses__():                        try:                                obj  =  cls.objects.get(baseobject_ptr=obj)                                break                        except  cls.DoesNotExist:                                continue                yield  obj
  16. 34.

    “Our site worked fine in development and testing, and was

    working wonderfully for the first few months. “But we just added a bunch more data, and now our homepage takes 27 seconds to load.”
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  18. 40.

    Abstract base classes don’t suffer from these performance problems. Denormalize

    into a UI-ordered auxiliary model. Non-relational databases work particular well here (I like SOLR). If you must get fancy:
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  20. 43.

    >>>  import  sys >>>  sys.path ['',  '/Library/Python/2.6/site-­‐packages/pip-­‐0.8-­‐py2.6.egg',  '/Library/Python/2.6/site-­‐packages/pdbpp-­‐0.7-­‐py2.6.egg',  '/Library/Python/2.6/site-­‐packages/Pygments-­‐1.4-­‐py2.6.egg',  '/Library/Python/2.6/site-­‐packages/wmctrl-­‐0.1-­‐py2.6.egg',

     '/Library/Python/2.6/site-­‐packages/pyrepl-­‐0.8.2-­‐py2.6.egg',  ...  '/System/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6',  ...  '/Users/jacob/.local/lib/python2.6/site-­‐packages',  '/Library/Python/2.6/site-­‐packages',  ...]
  21. 44.

    >>>  import  sys >>>  sys.path ['',  '/Library/Python/2.6/site-­‐packages/pip-­‐0.8-­‐py2.6.egg',  '/Library/Python/2.6/site-­‐packages/pdbpp-­‐0.7-­‐py2.6.egg',  '/Library/Python/2.6/site-­‐packages/Pygments-­‐1.4-­‐py2.6.egg',  '/Library/Python/2.6/site-­‐packages/wmctrl-­‐0.1-­‐py2.6.egg',

     '/Library/Python/2.6/site-­‐packages/pyrepl-­‐0.8.2-­‐py2.6.egg',  ...  '/System/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6',  ...  '/Users/jacob/.local/lib/python2.6/site-­‐packages',  '/Library/Python/2.6/site-­‐packages',  ...] >>>  import  re >>>  re <module  're'  from  '/System/Library/Frameworks/Python.framework/Versions/ 2.6/lib/python2.6/re.pyc'>
  22. 45.

    ~/Projects/djdash !""  __init__.py !""  dashboard $      !""  __init__.py

    $      !""  admin.py $      !""  models.py $      #""  views.py #""  manage.py (https://github.com/jacobian/django-dev-dashboard)
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  24. 51.

    $  ./manage.py  shell >>>  import  dashboard.models >>>  dashboard.models <module  'dashboard.models'

       from  '/Users/jacob/Projects/djdash/dashboard/models.pyc'> >>>  import  djdash.dashboard.models
  25. 52.

    $  ./manage.py  shell >>>  import  dashboard.models >>>  dashboard.models <module  'dashboard.models'

       from  '/Users/jacob/Projects/djdash/dashboard/models.pyc'> >>>  import  djdash.dashboard.models >>>  djdash.dashboard.models <module  'djdash.dashboard.models'  from  '/Users/jacob/Projects/djdash/../djdash/dashboard/models.pyc'>
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    $  ./manage.py  shell >>>  import  dashboard.models >>>  dashboard.models <module  'dashboard.models'

       from  '/Users/jacob/Projects/djdash/dashboard/models.pyc'> >>>  import  djdash.dashboard.models >>>  djdash.dashboard.models <module  'djdash.dashboard.models'  from  '/Users/jacob/Projects/djdash/../djdash/dashboard/models.pyc'> >>>  djdash.dashboard.models.Metric  is  dashboard.models.Metric
  27. 54.

    $  ./manage.py  shell >>>  import  dashboard.models >>>  dashboard.models <module  'dashboard.models'

       from  '/Users/jacob/Projects/djdash/dashboard/models.pyc'> >>>  import  djdash.dashboard.models >>>  djdash.dashboard.models <module  'djdash.dashboard.models'  from  '/Users/jacob/Projects/djdash/../djdash/dashboard/models.pyc'> >>>  djdash.dashboard.models.Metric  is  dashboard.models.Metric False
  28. 55.

    “Hey, many-to-many relations don’t show up in the admin.” “What’s

    up with these import errors when I deploy under mod_wsgi?” “Grrr… assertRaises doesn’t work!” You might have an import issue if…
  29. 57.

    Fixing import madness 1. Use non-project-relative imports (import  app.models, not

    import project.app.models). 2. Use relative imports (from  .  import  x) where possible (see http://bit.ly/pep328). 3. Stop using manage.py.
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    $  django-­‐admin.py  shell  -­‐-­‐pythonpath=`pwd`  -­‐-­‐settings=settings.local >>>  import  dashboard.models >>>  import

     djdash.dashboard.models Traceback  (most  recent  call  last) ... ImportError:  No  module  named  djdash.dashboard.models Delete manage.py?
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    $  django-­‐admin.py  shell  -­‐-­‐pythonpath=`pwd`  -­‐-­‐settings=settings.local >>>  import  dashboard.models >>>  import

     djdash.dashboard.models Traceback  (most  recent  call  last) ... ImportError:  No  module  named  djdash.dashboard.models Delete manage.py?
  32. 64.

    $  add2virtualenv  ~/Projects/djdash $  echo  "export  DJANGO_SETTINGS_MODULE=settings.local"  \    >>

     $VIRTUAL_ENV/bin/postactivate $  echo  "unset  DJANGO_SETTINGS_MODULE"  \    >>  $VIRTUAL_ENV/bin/postdeactivate $  django-­‐admin.py  shell For virtualenv users:
  33. 66.

    INSTALLED_APPS  +=  [p  for  p  in  os.listdir(BASE)      

                                   if  os.path.isdir(p)] Don’t do this …
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    urlpatterns  =  patterns('',  ...) for  app  in  settings.INSTALLED_APPS:    

       if  not  app.startswith('django'):                p  =  url('^%s/'  %  app,  include('%s.urls')  %  app)                urlpatterns  +=  patterns('',  p) … or this …
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    MIDDLEWARE_CLASSES  =  [...] def  callback(arg,  dirname,  fnames):      

     if  'middleware.py'  in  fnames:                m  =  '%s.middleware'  %  os.path.split(dirname)[-­‐1])                MIDDLEWARE_CLASSES.append(m) os.path.walk(BASE,  callback,  None) … or this.
  36. 70.

    INSTALLED_APPS  =  (        'django.contrib.auth',      

     'django.contrib.contenttypes',        'django.contrib.sessions',        'django.contrib.sites',        'django.contrib.messages',        'django.contrib.staticfiles',        'django.contrib.admin',        'django.contrib.flatpages',          'django_extensions',          'debug_toolbar',          'south',          'rs.users',          'rs.orgs',          'rs.signup',        'rs.clients',        'rs.timezones',        'rs.caregivers',        'rs.dashboard',        'rs.scripts',        'rs.reminders',        'rs.billing',        'rs.calls',        'chunks',        'contact_form', )
  37. 71.

    INSTALLED_APPS  =  (        'django.contrib.auth',      

     'django.contrib.contenttypes',        'django.contrib.sessions',        'django.contrib.sites',        'django.contrib.messages',        'django.contrib.staticfiles',        'django.contrib.admin',        'django.contrib.flatpages',          'django_extensions',          'debug_toolbar',          'south',          'rs.users',          'rs.orgs',          'rs.signup',        'rs.clients',        'rs.timezones',        'rs.caregivers',        'rs.dashboard',        'rs.scripts',        'rs.reminders',        'rs.billing',        'rs.calls',        'chunks',        'contact_form', ) urlpatterns  =  patterns('',        url(r'^admin/',  include(admin.site.urls)),        url(r'^signup/',  include('rs.signup.urls')),        url(r'^org/',  include('rs.orgs.urls')),          url(r'^clients/',  include('rs.clients.urls')),        url(r'^caregivers/',  include('rs.caregivers.urls')),        url(r'^account/',  include('rs.users.urls')),        url(r'^dashboard/',  include('rs.dashboard.urls')),        url(r'^reminders/',  include('rs.reminders.urls')),        url(r'^calls/',  include('rs.calls.urls')),        url(r'^scripts/',  include('rs.scripts.urls')),        url(r'^contact/',  include('contact_form.urls')),          url(r'^login/',  'django.contrib.auth.views.login',  {},  'login'),          url(r'^logout/$',  'django.contrib.auth.views.logout',  {},  'logout',),        url(r'^changepassword/$',  'django.contrib.auth.views.password_change') )
  38. 72.

    INSTALLED_APPS  =  (        'django.contrib.auth',      

     'django.contrib.contenttypes',        'django.contrib.sessions',        'django.contrib.sites',        'django.contrib.messages',        'django.contrib.staticfiles',        'django.contrib.admin',        'django.contrib.flatpages',          'django_extensions',          'debug_toolbar',          'south',          'rs.users',          'rs.orgs',          'rs.signup',        'rs.clients',        'rs.timezones',        'rs.caregivers',        'rs.dashboard',        'rs.scripts',        'rs.reminders',        'rs.billing',        'rs.calls',        'chunks',        'contact_form', ) urlpatterns  =  patterns('',        url(r'^admin/',  include(admin.site.urls)),        url(r'^signup/',  include('rs.signup.urls')),        url(r'^org/',  include('rs.orgs.urls')),          url(r'^clients/',  include('rs.clients.urls')),        url(r'^caregivers/',  include('rs.caregivers.urls')),        url(r'^account/',  include('rs.users.urls')),        url(r'^dashboard/',  include('rs.dashboard.urls')),        url(r'^reminders/',  include('rs.reminders.urls')),        url(r'^calls/',  include('rs.calls.urls')),        url(r'^scripts/',  include('rs.scripts.urls')),        url(r'^contact/',  include('contact_form.urls')),          url(r'^login/',  'django.contrib.auth.views.login',  {},  'login'),          url(r'^logout/$',  'django.contrib.auth.views.logout',  {},  'logout',),        url(r'^changepassword/$',  'django.contrib.auth.views.password_change') ) MIDDLEWARE_CLASSES  =  (        'django.middleware.common.CommonMiddleware',        'django.contrib.sessions.middleware.SessionMiddleware',        'django.middleware.csrf.CsrfViewMiddleware',        'django.contrib.auth.middleware.AuthenticationMiddleware',        'django.contrib.messages.middleware.MessageMiddleware',        'django.contrib.flatpages.middleware.FlatpageFallbackMiddleware',        'debug_toolbar.middleware.DebugToolbarMiddleware', )
  39. 74.

    At the bottom of your settings file: try:    

       from  local_settings  import  * except  ImportError:        pass The localsettings anti-pattern
  40. 75.

    “It’s simple: just create a local_settings.py, throw overridden settings in

    there, and then never check the file into source control.”
  41. 76.

    “It’s simple: just create a local_settings.py, throw overridden settings in

    there, and then never check the file into source control.”
  42. 79.

    1. Don’t. Why is your staging environment different from production?

    2. Use DJANGO_SETTINGS_MODULE. Handling multiple settings files
  43. 81.

    settings !""  __init__.py !""  base.py !""  staging.py !""  production.py #""

     local.py The one true way #  base.py INSTALLED_APPS  =  [...] #  local.py from  settings.base  import  * INSTALLED_APPS  +=  ['debug_toolbar']
  44. 82.

    settings !""  __init__.py !""  base.py !""  staging.py !""  production.py #""

     local.py The one true way #  base.py INSTALLED_APPS  =  [...] #  local.py from  settings.base  import  * INSTALLED_APPS  +=  ['debug_toolbar'] $  django-­‐admin.py  shell  -­‐-­‐settings=settings.local
  45. 83.

    settings !""  __init__.py !""  base.py !""  staging.py !""  production.py #""

     local.py The one true way #  base.py INSTALLED_APPS  =  [...] #  local.py from  settings.base  import  * INSTALLED_APPS  +=  ['debug_toolbar'] $  django-­‐admin.py  shell  -­‐-­‐settings=settings.local #  deploy.wsgi os.environ['DJANGO_SETTINGS_MODULE']  =  'settings.deploy'