Hunting For Treasure In Django

Transcript

1. Hunting for Treasure
   in Django
   Sebastian Vetter
   @elbaschid
   

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2. Who Am I?
   

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

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4. What's The Treasure?
   

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

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6. But They Are Boring
   

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7. Real Treasure
   

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

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

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11. cached_property
    

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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.
    

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

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

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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)
    

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16. Here's the problem
    • Using the name attribute will call the API
    • Every time!
    

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

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18. 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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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)
    

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

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21. Isn't That Great
    

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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
    

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23. import_string
    

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

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

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26. 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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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_!']
    

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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
    

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29. lazy and
    lazy_property
    

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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.
    

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

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32. 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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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.
    

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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
    

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35. RequestFactory
    

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36. 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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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)
    

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38. 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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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
    

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40. The Treasure Is Yours
    

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

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