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Demystifying Mixins with Django

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@anabalica

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I work at Potato

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Mixins are a controlled way of adding functionality to classes.

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Mixins are not special language constructs.

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In fact, mixins are ordinary Python classes. 1 class SomeMixin(object): 2 """My smart mixin""" 3 4 def test_method(self): 5 pass

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Why use mixins? to improve modularity

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When to use mixins? want to reuse a particular feature in a lot of different classes

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Properties • single responsibility • not meant to be extended • not meant to be instantiated

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In Python the concept of mixins is implemented using multiple inheritance.

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Order matters

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1 class Foo(BaseFoo, SomeMixin): 2 pass

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1 class Foo(BaseFoo, SomeMixin): 2 pass base class

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1 class Foo(BaseFoo, SomeMixin): 2 pass base class mixin

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1 class Foo(BaseFoo, SomeMixin): 2 pass

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1 class Foo(SomeMixin, BaseFoo): 2 pass

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1 class Foo(SomeMixin, BaseFoo): 2 pass

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1 # some_app/views.py 2 from django.views.generic import TemplateView 3 4 5 class AboutView(TemplateView): 6 template_name = "about.html"

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1 # some_app/views.py 2 from django.views.generic import TemplateView 3 4 5 class AboutView(SomeMixin, TemplateView): 6 template_name = "about.html"

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1 # some_app/views.py 2 from django.views.generic import TemplateView 3 4 5 class AboutView(SomeMixin, TemplateView): 6 template_name = "about.html"

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My first mixin

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1 # some_app/views.py 2 3 4 class LoginRequiredMixin(object): 5

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1 # some_app/views.py 2 3 4 class LoginRequiredMixin(object): 5 6 def dispatch(self, request, *args, **kwargs): 7

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1 # some_app/views.py 2 from django.core.exceptions import PermissionDenied 3 4 5 class LoginRequiredMixin(object): 6 7 def dispatch(self, request, *args, **kwargs): 8 if not request.user.is_authenticated(): 9 raise PermissionDenied 10

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1 # some_app/views.py 2 from django.core.exceptions import PermissionDenied 3 4 5 class LoginRequiredMixin(object): 6 7 def dispatch(self, request, *args, **kwargs): 8 if not request.user.is_authenticated(): 9 raise PermissionDenied 10 11 return super(LoginRequiredMixin, self).\ 12 dispatch(request, *args, **kwargs) 13

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1 # some_app/views.py 2 from django.views.generic import TemplateView 3 4 5 class AboutView(LoginRequiredMixin, TemplateView): 6 template_name = "about.html"

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LoginRequiredMixin TemplateView AboutView

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LoginRequiredMixin DetailView AboutView

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TemplateView LoginRequiredTemplateView AboutView ListView LoginRequiredListView AboutView CreateView LoginRequiredCreateView AboutView DetailView LoginRequiredDetailView AboutView FormView LoginRequiredFormView AboutView MyView LoginRequiredMyView AboutView

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LoginRequiredMixin TemplateView AboutView

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dispatch() get_context_data() get_template_names() check if user is logged in, has permission add new data to the context add more flexibility to the template names

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1 # some_app/views.py 2 from django.views.generic import TemplateView 3 4 5 class AboutView(TemplateView): 6 template_name = "about.html"

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dispatch() get_context_data() get_template_names() check if user is logged in, has permission add new data to the context add more flexibility to the template names

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docs.djangoproject.com/en/1.8/ref/ class-based-views/base/

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docs.djangoproject.com/en/1.8/ref/ class-based-views/base/

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docs.djangoproject.com/en/1.8/topics/ class-based-views/mixins/

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docs.djangoproject.com/en/1.8/topics/ class-based-views/mixins/

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ccbv.co.uk/

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django-braces Access Mixins Form Mixins Other Mixins

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Decorators login_required() user_passes_test() permission_required()

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Good news everyone!

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Django 1.9 LoginRequiredMixin UserPassesTestMixin PermissionRequiredMixin

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Runtime magic

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1 class CuteMixin: 2 def be_cute(self): 3 print "{} ✿♥‿♥✿".format(self.name) 4 py2

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1 class CuteMixin: 2 def be_cute(self): 3 print "{} ✿♥‿♥✿".format(self.name) 4 5 6 class Mascot: 7 def __init__(self, name): 8 self.name = name 9 py2

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1 class CuteMixin: 2 def be_cute(self): 3 print "{} ✿♥‿♥✿".format(self.name) 4 5 6 class Mascot: 7 def __init__(self, name): 8 self.name = name 9 10 11 if __name__ == '__main__': 12 domo = Mascot("Domo-kun") 13 Mascot.__bases__ += (CuteMixin, ) 14 domo.be_cute() py2

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1 class CuteMixin: 2 def be_cute(self): 3 print "{} ✿♥‿♥✿".format(self.name) 4 5 6 class Mascot: 7 def __init__(self, name): 8 self.name = name 9 10 11 if __name__ == '__main__': 12 domo = Mascot("Domo-kun") 13 Mascot.__bases__ += (CuteMixin, ) 14 domo.be_cute() py2

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Domo-kun ✿♥‿♥✿

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1 class CuteMixin: 2 def be_cute(self): 3 print "{} ✿♥‿♥✿".format(self.name) 4 5 6 class Mascot: 7 def __init__(self, name): 8 self.name = name 9 10 11 if __name__ == '__main__': 12 domo = Mascot("Domo-kun") 13 Mascot.__bases__ += (CuteMixin, ) 14 domo.be_cute() py2

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1 class CuteMixin: 2 def be_cute(self): 3 print(“{} ✿♥‿♥✿”.format(self.name)) 4 5 6 class Mascot: 7 def __init__(self, name): 8 self.name = name 9 py3

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1 class CuteMixin: 2 def be_cute(self): 3 print "{} ✿♥‿♥✿".format(self.name) 4 5 6 class Mascot: 7 def __init__(self, name): 8 self.name = name 9 10 11 if __name__ == '__main__': 12 kumamon = Mascot("Kumamon") 13 kumamon.__class__ = type('SomeNewType', 14 (Mascot, CuteMixin), {}) 15 kumamon.be_cute() py3

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1 class CuteMixin: 2 def be_cute(self): 3 print "{} ✿♥‿♥✿".format(self.name) 4 5 6 class Mascot: 7 def __init__(self, name): 8 self.name = name 9 10 11 if __name__ == '__main__': 12 kumamon = Mascot("Kumamon") 13 kumamon.__class__ = type('SomeNewType', 14 (Mascot, CuteMixin), {}) 15 kumamon.be_cute() py3

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Kumamon ✿♥‿♥✿

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With great power comes great responsibility

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Recap • single responsibility • plug-in functionality • isn’t creating a subtyping relation

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Go back to your views and start writing mixins to clean up the code.