Hunting For Treasure In Django

Transcript

1. Hunting for Treasure in Django Sebastian Vetter @elbaschid
2. Who Am I?
3. Sebastian • Django & Python Developer • Backend Engineer @ Mobify • github/twitter: elbaschid
4. What's The Treasure?
5. Awesome Django Features • Forms, • Views, • Models, • the ORM, or • other commonly used APIs.
6. But They Are Boring
7. Real Treasure
8. What Does That Mean? • Useful pieces of Django code. • Considered public API. • Documentation is available (sort of). • Mainly used within Django itself.
9. My Hunting Strategy • Digging through the Django source. • Hanging out with Funkybob. • Learning from other great people.
10. What I'll Do • Show a few "hidden" treasures. • Explain what they do. • Look at examples.
11. cached_property
12. 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.
13. What does it do? • It's a decorator. • Caches the return value. • Lives as long as the instance.
14. It looks like this class MyObject(object): @cached_property def compute_heavy_method(self): ... return result
15. 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)
16. Here's the problem • Using the name attribute will call the API • Every time!
17. Here's the problem >>> c = Color('ffffff') >>> c.name Requesting #ffffff white >>> c.name Requesting #ffffff white
18. Possible solution @property def name(self): if self._name is None: self._name = self._request_colour_name(self.hex) return self._name
19. 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)
20. Using the cached property >>> c = Color('ffffff') >>> c.name Requesting #ffffff white >>> c.name white
21. Isn't That Great
22. 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
23. import_string
24. Where is it useful? • Make a class or function configurable. • Allow loading class/function from string.
25. What does it do? • Takes dotted path to a class or function. • Loads it. • Returns the class or function object.
26. It looks like this from django.utils.module_loading import import_string get_func = import_string('requests.get') print get_func # <function requests.api.get> get_func('https://google.ca') # <Response [200]>
27. # settings.py UPLOAD_VALIDATION_PIPELINE = [ 'my_project.uploads.validators.is_tarball', 'my_project.uploads.validators.has_readme_file', 'my_project.uploads.validators.has_no_!']
28. 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
29. lazy and lazy_property
30. Where is it useful? • Accessing settings at parse time, e.g. class attributes. • Translating strings outside of a view. • Translations in the settings module.
31. Here's a problem class UserSignupView(CreateView): ... success_url = reverse('signup-confirmed')
32. How can we fix it? from django.utils.functional import lazy class UserSignupView(CreateView): ... success_url = lazy(reverse('signup-confirmed'), unicode)
33. Lazy Django • The Settings object is lazy. • Several helpers have lazy siblings: • reverse_lazy • ugettext_lazy • Not sure what lazy_property is useful for.
34. 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
35. RequestFactory
36. Where Is It Useful? • Testing request related code. • Mocking will be too much work. • Using the test client doesn't make sense.
37. 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)
38. Create POST Request from django.test import RequestFactory post_params = {'username':'testuser', 'password':'supersecret'} request = RequestFactory().post('/login', data=post_params)
39. 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
40. The Treasure Is Yours
41. Thanks! Questions? • www.roadsi.de • @elbaschid • github.com/elbaschid Slides: https://speakerdeck.com/elbaschid