Hunting For Treasure In Django

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Hunting for Treasure in Django Sebastian Vetter @elbaschid

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Who Am I?

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Sebastian • Django & Python Developer • Backend Engineer @ Mobify • github/twitter: elbaschid

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What's The Treasure?

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

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But They Are Boring

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Real Treasure

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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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My Hunting Strategy • Digging through the Django source. • Hanging out with Funkybob. • Learning from other great people.

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What I'll Do • Show a few "hidden" treasures. • Explain what they do. • Look at examples.

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cached_property

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Where is it useful? • Time or compute heavy properties on a class. • Synchronous calls to remote servers. • Used more than once, e.g. code & template.

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What does it do? • It's a decorator. • Caches the return value. • Lives as long as the instance.

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It looks like this class MyObject(object): @cached_property def compute_heavy_method(self): ... return result

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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 • Using the name attribute will call the API • Every time!

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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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Possible solution @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 you can use cached_property from django.utils.functional import cached_property @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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Isn't That Great

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All you Need To Know from django.utils.functional import cached_property • Only cached for the lifetime of the instance. • Be careful with querysets. • Django docs • Source

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import_string

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Where is it useful? • Make a class or function conﬁgurable. • Allow loading class/function from string.

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What does it do? • Takes dotted path to a class or function. • Loads it. • Returns the class or function object.

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It looks like this 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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# settings.py UPLOAD_VALIDATION_PIPELINE = [ 'my_project.uploads.validators.is_tarball', 'my_project.uploads.validators.has_readme_file', 'my_project.uploads.validators.has_no_!']

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All you Need To Know from django.utils.module_loading import import_string • Imports a class or function from a dotted path. • Django docs • Source

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lazy and lazy_property

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Where is it useful? • Accessing settings at parse time, e.g. class attributes. • Translating strings outside of a view. • Translations in the settings module.

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Here's a problem class UserSignupView(CreateView): ... success_url = reverse('signup-confirmed')

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How can we fix it? from django.utils.functional import lazy class UserSignupView(CreateView): ... success_url = lazy(reverse('signup-confirmed'), unicode)

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Lazy Django • The Settings object is lazy. • Several helpers have lazy siblings: • reverse_lazy • ugettext_lazy • Not sure what lazy_property is useful for.

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All you Need To Know from django.utils.functional import lazy from django.utils.functional import SimpleLazyObject • Imports a class or function from a dotted path. • Django docs • Source

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RequestFactory

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Where Is It Useful? • Testing request related code. • Mocking will be too much work. • Using the test client doesn't make sense.

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Create GET Request from django.test import RequestFactory request = RequestFactory().get('/some/path') # with a query string query_params = {"token": "secret-token"} request = RequestFactory().get('/some/path', data=query_params)

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Create POST Request from django.test import RequestFactory post_params = {'username':'testuser', 'password':'supersecret'} request = RequestFactory().post('/login', data=post_params)

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All you Need To Know 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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The Treasure Is Yours

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Thanks! Questions? • www.roadsi.de • @elbaschid • github.com/elbaschid Slides: https://speakerdeck.com/elbaschid