Hunting for Treasure in Django

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Hunting for Treasure in Django Sebastian Vetter @elbaschid

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Sebastian Vetter » Django & Python Developer » Backend Engineer @ Mobify in Vancouver ! » @elbaschid on github & twitter » Slides: http://bit.ly/treasure-hunt

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Let's Find Some Treasure

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Awesome Django Features » Forms, » Views, » Models, » the ORM, or » other commonly used APIs.

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An Old Hat

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Hidden Treasures

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What Does That Mean? » Useful pieces of Django code. » Considered public API. » Documentation is available (sort of). » Mainly used within Django itself.

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Where To Find Them

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Where You Find Them » Digging through the Django source. » Working with great & smart people. » Hanging out in the IRC channel. » Sprinting at Conferences.

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Ready?

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cached_property

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What It Does » It's a decorator. » Caches property's return value. » Lives as long as the instance.

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What It Looks Like class MyObject(object): @cached_property def compute_heavy_method(self): ... return result

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Where It Is Useful » Compute-heavy properties on a class. » Calling web APIs. » Property used more than once.

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Imagine A Color API class Color(object): def __init__(self, hex): self.hex = hex def _request_colour_name(self, hex): print "Requesting #{}".format(hex) rsp = requests.get(API_ENDPOINT.format(hex)) return rsp.json()[0].get("title") @property def name(self): return self._request_colour_name(self.hex)

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Here's the problem >>> c = Color('ffffff') >>> c.name Requesting #ffffff white >>> c.name Requesting #ffffff white

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You Can DIY it @property def name(self): if self._name is None: self._name = self._request_colour_name(self.hex) return self._name

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Or Use cached_property from django.utils.functional import cached_property class Some(object): ... @cached_property def name(self): return self._request_colour_name(self.hex)

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Using the cached property >>> c = Color('ffffff') >>> c.name Requesting #ffffff white >>> c.name white

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Beware Of Querysets » Be careful with querysets. class VeryComplicatedView(object): @cached_property def get_followers(self): return User.objects.ﬁlter(followed_by=self.user)

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In Short from django.utils.functional import cached_property » Django docs » Source

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Treasure Found

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import_string

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What It Does » Takes dotted path to a class or function. » Validates and loads it. » Returns the class or function object.

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What It Looks Like from django.utils.module_loading import import_string get_func = import_string('requests.get') print get_func ## get_func('https://google.ca') ##

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Where It Is Useful » Make a class or function conﬁgurable. » Custom implementation in libraries.

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Imagine A Web Store » Products have a "slug". » But you want it to be customizable. # settings.py CUSTOM_SLUG_FUNCTION = 'my_store.!"#$_slugiﬁer'

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Slugify Is Easy Now # utils.py def slugify(value): slugifier = getattr(settings, 'CUSTOM_SLUG_FUNCTION', DEFAULT_SLUG_FUNCTION) slugifier = import_string(slugifier) return slugifier(value)

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In Short from django.utils.module_loading import import_string » Imports a class or function from a dotted path. » Previously known as import_by_path. » Django docs » Source

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More Treasure

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lazy & LazyObject

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What It Does » Delays execution of the wrapped callable. » Used for the Django settings module.

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Where It Is Useful » Accessing settings at parse time. » Translating strings outside of a view. » Translations in the settings module.

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What It Looks Like from django.utils.functional import lazy from django.core.urlresolvers import reverse reverse_lazy = lazy(reverse('home'), unicode))

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Imagine per-User Storage class PrivateMediaStorage(S3Storage): ... class AwesomeThing(models.Model): ﬁle = models.FileField(..., storage=PrivateMediaStorage()) ...

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Kaboom

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lazy To The Rescue def get_private_storage(): return PrivateMediaStorage() private_storage = SimpleLazyObject(get_private_storage) class AwesomeThing(models.Model): ﬁle = models.FileField(..., storage=private_storage) ...

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In Short from django.utils.functional import lazy from django.utils.functional import SimpleLazyObject » Acts as a proxy class or function. » Delays execution of the wrapped object. » Django docs » Source

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And Even More Treasure

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RequestFactory

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What It Does » Takes a URL with a HTTP method. » Creates an actual Request object.

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What It Looks Like from django.test import RequestFactory request = RequestFactory().get('/some/path')

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Where It Is Useful » Testing request-related code. » Mocking will be too much work.

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Imagine A Middleware class SomeMiddleware(object): def process_request(self, request): ...

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How To Test It from django.test import RequestFactory def test_processing_requests(): factory = RequestFactory() query_params = {"token": "secret-token"} request = RequestFactory().get('/some/path', data=query_params) SomeMiddleware.process_request(request) ...

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In Short from django.test import RequestFactory » Creates a fake request for given URL. » Can handle all HTTP methods. » Will save you some mocking work. » Django docs » Source

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Treasure Found

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method_decorator

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What It Does » It's another decorator. » Apply decorators to methods.

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What It Looks Like class AboutPage(TemplateView): @method_decorator(function_decorator) def dispatch(self, request, *args, **kwargs): ...

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Where It Is Useful » Use function decorators on views. » Decorate dispatch on a view without extending it.

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What It Looks Like from waffle.decorators import waffle_flag class NewFeatureView(TemplateView): ... @method_decorator(waffle_flag('new-feature')) def dispatch(self, request, *args, **kwargs): return super().dispatch(request, *args, **kwargs)

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Or Like This from waffle.decorators import waffle_flag @method_decorator(waffle_flag('new-feature'), name='dispatch') class NewFeatureView(TemplateView): ...

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In Short from django.utils.functional import method_decorator » Django docs » Source

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The Treasure Is All Yours

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Any Questions? » @elbaschid Slides: http://bit.ly/treasure-hunt

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References (I) » https://www.flickr.com/photos/kohlerfolk/ 2189799465 » https://www.flickr.com/photos/ 28912254@N04/16532668296/ » https://www.flickr.com/photos/bernatcg/1123973353/ » https://flic.kr/p/93mN4L » https://www.flickr.com/photos/ 8015956@N04/10012870693/ » http://wallpapercave.com/wp/prPWzge.jpg

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References (II) » https://www.flickr.com/photos/vandinglewop/ 6104500070/ » https://www.flickr.com/photos/xtrah/5005443977 » https://www.flickr.com/photos/chezpitch/ 6703950199/ » https://flic.kr/p/9qy7dG » https://www.flickr.com/photos/epsos/8463683689