Advanced Django Forms Usage

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Advanced Django Form Usage by Daniel Greenfeld and Miguel Araujo

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Advanced Django Form Usage @pydanny / @maraujop Daniel Greenfeld • pydanny • Python & Django developer for Cartwheel Web / RevSys • Founded django-uni-form • Does Capoeira • Lives in Los Angeles with his Fiancé, Audrey Roy (audreyr) http://www.ﬂickr.com/photos/pydanny/4442245488/ 2

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Advanced Django Form Usage @pydanny / @maraujop Miguel Araujo • maraujop • Freelance Python developer • Co-lead of django-uni-form • Does Muay Thai • Lives in Madrid with his amazing girlﬁend who does aerospace for a living • http://maraujop.github.com/ 3

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Advanced Django Form Usage @pydanny / @maraujop Tons of technical content • We probably won’t have time for questions • Slides will be posted right after the talk • Too much content in the abstract • Special thanks to: • Brian Rosner • James Tauber • Frank Wiles 4

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Advanced Django Form Usage @pydanny / @maraujop Fundamentals of Good Form Patterns • Zen of Python still applies • import this • Spartan programming als0 is important 5

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Advanced Django Form Usage @pydanny / @maraujop Spartan Programming • Horizontal complexity • Vertical complexity (line count) • Token count • Character count • Variables • Loops • Conditionals 6 http://www.codinghorror.com/blog/2008/07/spartan-programming.html

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Advanced Django Form Usage @pydanny / @maraujop Spartan Programming • Horizontal complexity • Vertical complexity (line count) • Token count • Character count • Variables • Loops • Conditionals 7 http://www.codinghorror.com/blog/2008/07/spartan-programming.html

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Advanced Django Form Usage @pydanny / @maraujop Spartan Programming • Horizontal complexity • Vertical complexity (line count) • Token count • Character count • Variables • Loops • Conditionals 8 http://www.codinghorror.com/blog/2008/07/spartan-programming.html

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Advanced Django Form Usage @pydanny / @maraujop Calling forms the easy way • Smaller, cleaner code makes our lives better • Line 5 of the Zen of Python • Flat is better than nested. • Aim for minimal boilerplate • So you can focus on your business logic 9

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Enough theory

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Advanced Django Form Usage @pydanny / @maraujop A Basic Django Form 11 class MyForm(forms.Form): name = forms.CharField(_('Name'), required=True)

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Advanced Django Form Usage @pydanny / @maraujop Standard views.py 12 def my_view(request, template_name='myapp/my_form.html'): if request.method == 'POST': form = MyForm(request.POST) # Form #1! if form.is_valid(): # nested if! do_x() return redirect('/') else: form = MyForm() # Form #2! return render(request, template_name, {'form': form}) Form #1 Form #2 Only 1 nested if, but real code gets much more complex Custom business goes here

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Advanced Django Form Usage @pydanny / @maraujop Easy views.py 13 def my_view(request, template_name='myapp/my_form.html'): # sticks in a POST or renders empty form form = MyForm(request.POST or None) if form.is_valid(): do_x() return redirect('home') return render(request, template_name, {'form': form}) Single form Custom business goes here If no request.POST, then instantiated with None

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Advanced Django Form Usage @pydanny / @maraujop def my_view(request, template_name='myapp/my_form.html'): # sticks in a POST or renders empty form form = MyForm(request.POST or None) if form.is_valid(): do_x() return redirect('home') return render(request, template_name, {'form': form}) Easy views.py • 6 lines of code instead of 9 • 33.3333333333% less code to debug • One form instantiation • less conditionals == less edge case insanity 14

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What about ﬁle uploads?

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Advanced Django Form Usage @pydanny / @maraujop Easy views.py + ﬁles • 6 lines of code again! • Code donated by Audrey Roy 16 def my_view(request, template_name='myapp/my_form.html'): form = MyForm(request.POST or None, request.FILES or None) if form.is_valid(): do_x() return redirect('home') return render(request, template_name, {'form': form}) Request.POST or None Request.FILES or None

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What about ModelForms?

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Advanced Django Form Usage @pydanny / @maraujop pydanny made up statistics • 91% of all Django projects use ModelForms • 80% ModelForms require trivial logic • 20% ModelForms require complicated logic 18 Let’s try and make that easy

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Advanced Django Form Usage @pydanny / @maraujop A Basic ModelForm 19 class MyModelForm(forms.Form): class Meta: model = MyModel fields = ['name']

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Advanced Django Form Usage @pydanny / @maraujop Classic views.py for ModelForm 20 def my_model_edit(request, slug=slug, template_name='myapp/my_model_form.html'): # I wouldn't call the variable model, because it's an instance of a model, it's confusing mymodel = get_object_or_404(MyModel, slug=slug) if request.method == 'POST': form = MyForm(request, instance=mymodel) if form.is_valid(): mymodel = form.save() mymodel.day_shown = datetime.datetime.now() # Do any extra model stuff here mymodel.save() return redirect('home') else: form = MyForm(instance=mymodel) return render(request, template_name, {'form': form, 'model': mymodel}) Form #1 Form #2 Only 1 nested if, but real code gets much more complex Custom business goes here

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Advanced Django Form Usage @pydanny / @maraujop Classic views.py for ModelForm 21 def my_model_edit(request, slug=slug, template_name='myapp/my_model_form.html'): # I wouldn't call the variable model, because it's an instance of a model, it's confusing mymodel = get_object_or_404(MyModel, slug=slug) if request.method == 'POST': form = MyForm(request, instance=mymodel) if form.is_valid(): mymodel = form.save() mymodel.day_shown = datetime.datetime.now() # Do any extra model stuff here mymodel.save() return redirect('home') else: form = MyForm(instance=mymodel) return render(request, template_name, {'form': form, 'model': mymodel}) • 12 lines of code • Nested conditionals • What if we have to handle 3 diﬀerent submit buttons? • Watch out for edge case insanity!

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Advanced Django Form Usage @pydanny / @maraujop easy views.py + ModelForm 22 def my_model_edit(request, slug=slug, template_name='myapp/ my_model_form.html'): mymodel = get_object_or_404(MyModel, slug=slug) form = MyModelForm(request.POST or None, instance=mymodel) if form.is_valid(): mymodel = form.save() mymodel.edited_at_djangocon = True mymodel.save() return redirect('home') return render(request, template_name, {'form': form, 'mymodel': mymodel}) Single form Custom business goes here If no request.POST, then instantiated with None So this will fail validation!

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Advanced Django Form Usage @pydanny / @maraujop easy views.py + ModelForm • 9 lines of code instead of 12 • One conditional • clear and succinct code 23 def my_model_edit(request, slug=slug, template_name='myapp/ my_model_form.html'): mymodel = get_object_or_404(MyModel, slug=slug) form = MyModelForm(request.POST or None, instance=mymodel) if form.is_valid(): mymodel = form.save() mymodel.edited_at_djangocon = True mymodel.save() return redirect('home') return render(request, template_name, {'form': form, 'mymodel': mymodel})

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What about new model instances?

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Advanced Django Form Usage @pydanny / @maraujop add views.py + ModelForm 25 def my_model_add(request, template_name='myapp/my_model_form.html'): form = MyModelForm(request.POST or None) if form.is_valid(): mymodel = form.save() mymodel.added_at_djangocon = True mymodel.save() return redirect('home') return render(request,template_name,{'form': form,'mymodel':mymodel}) No need for an instance here This creates the model instance.

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Advanced Django Form Usage @pydanny / @maraujop I can make it smaller! 26 def my_model_tiny_add(request,template_name='myapp/my_model_form.html'): form = MyModelForm(request.POST or None) if form.is_valid(): form.save() return redirect('home') return render(request,template_name,{'form':form,'mymodel':mymodel}) Good practice: Use model ﬁeld defaults rather than doing it in your views. Not setting defaults here

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How do you test this stuff?

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Advanced Django Form Usage @pydanny / @maraujop Please don’t manually test your forms • This isn’t a testing talk but... • Forms are the number one thing to test • Don’t skip on testing them • Edge case insanity is the thing to fear 28

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Advanced Django Form Usage @pydanny / @maraujop Django unit tests! 29 def test_add_package_view(self): url = reverse('my-url') response = self.client.get(url) self.assertEqual(response.status_code, 200) self.assertTemplateUsed(response, 'package/package_form.html') for c in Category.objects.all(): self.assertContains(response, c.title) count = Package.objects.count() response = self.client.post(url, { 'category': Category.objects.all()[0].pk, 'repo_url': 'http://github.com/django/django', 'slug': 'test-slug', 'title': 'TEST TITLE', }, follow=True) self.assertEqual(Package.objects.count(), count + 1) self.assertContains(response, "Django") POSTing a form follow=True assertContains is your best friend

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Can we change non-required to required?

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Advanced Django Form Usage @pydanny / @maraujop non-required to required • Your model ﬁelds are non-required • but you want the form ﬁelds to be required 31

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Advanced Django Form Usage @pydanny / @maraujop A basic Django models.py 32 class MyModel(models.Model): name = models.CharField(_('Name'), max_length=50, blank=True, null=True) age = models.IntegerField(_('Age in years'), blank=True, null=True) profession = models.CharField(_('Profession'), max_length=100, blank=True, null=True) bio = models.TextField(_('Bio'), blank=True, null=True)

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Advanced Django Form Usage @pydanny / @maraujop Classic forms.py overload 33 class MyModelTooMuchTypingForm(forms.ModelForm): """ I've done this and it sucks hard to debug and too much duplication """ name = forms.CharField(_('Name'), max_length=50, required=True) age = forms.IntegerField(_('Age in years'), required=True) profession = forms.CharField(_('Profession'), required=True) bio = forms.TextField(_('Bio'), required=True) class Meta: model = MyModel class MyModel(models.Model): name = models.CharField(_('Name'), max_length=50, blank=True, null=True) age = models.IntegerField(_('Age in years'), blank=True, null=True) profession = models.CharField(_('Profession'), max_length=100, blank=True, null=True) bio = models.TextField(_('Bio'), blank=True, null=True) Nearly duplicated code

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Advanced Django Form Usage @pydanny / @maraujop Better forms.py overload 34 class MyModelForm(forms.ModelForm): """ Much better and you are extending, not copy/pasting """ def __init__(self): super(MyModelForm, self).__init__(*args, **kwargs) self.fields['name'].required = True self.fields['age'].required = True self.fields['profession'].required = True self.fields['profession'].help_text = _("Hi professor") class Meta: model = MyModel Fields are in a dict-like object

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Advanced Django Form Usage @pydanny / @maraujop Try it with inheritance! 35 class BaseEmailForm(forms.Form): email = forms.EmailField(_('Email')) confirm_email = forms.EmailField(_('Email 2')) class ContactForm(BaseEmailForm): message = forms.CharField(_('Message')) def __init__(self): super(ContactForm, self).__init__(*args, **kwargs) self.fields['confirm_email'].label = _('Confirm your email') self.fields['confirm_email'].description = _('We want to be absolutely \ certain we have your correct email address.')

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Add dynamic ﬁelds to a form

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Advanced Django Form Usage @pydanny / @maraujop Dynamically adding ﬁelds to a form 37 def my_view(request, template_name='myapp/my_model_form.html'): form = MyModelForm(request.POST or None) # Let's add a field on the go, needs to be done before validating it form.fields['favorite_color'] = forms.ChoiceField( label = "Which is your favorite color from these?", choices = (('blue', 'blue'), ('red', 'red'), ('green', 'green')), widget = forms.RadioSelect, required = True, ) if form.is_valid(): # Let's get user's favorite color, # you can do whatever you want with it favorite_color = form.cleaned_data['favorite_color'] form.save() return redirect('home') return render(request, template_name, {'form': form}) Form dictionary of ﬁelds Fields have to be added before the form.is_valid method is checked.

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Can’t we just pass in a list of ﬁelds into a form from a view?

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Advanced Django Form Usage @pydanny / @maraujop Constructor overrides forms.py 39 class MyModelForm(forms.ModelForm): def __init__(self, *args, **kwargs): extra = kwargs.pop('extra') super(UserCreationForm, self).__init__(*args, **kwargs) for i, question in enumerate(extra): self.fields['custom_%s' % i] = forms.CharField(label=question) def extra_fields(self): """ Returns a tuple (question, answer) """ for name, value in self.cleaned_data.items(): if name.startswith('custom_'): yield (self.fields[name].label, value) looping over ‘extra’ iterable

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Advanced Django Form Usage @pydanny / @maraujop Constructor overrides views.py 40 def my_view(request, template_name='myapp/my_model_form.html'): form = MyModelForm(request.POST or None, extra=["What's your pet's name?"]) if form.is_valid(): # We can gather extra fields data doing for (question, answer) in form.extra_fields(): save_answer(request, question, answer) form.save() return redirect('home') return render(request, template_name, {'form': form}) Passing in a list of form ﬁeld titles

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I need a formset

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Advanced Django Form Usage @pydanny / @maraujop class ItemFormSet(BaseFormSet): def __init__(self, numberItems, *args, **kwargs): super(ItemFormSet, self).__init__(*args, **kwargs) self.numberItems = numberItems def clean(self): # Don't bother validating the formset # unless each form is valid on its own if any(self.errors): return for form in self.forms: if not form.cleaned_data['your_choice'] == 'mod_wsgi': raise ValidationError(u'mod_wsgi is the way to go!') formsets.py 42 Forms must have ‘your_choice’ ﬁeld that only accepts “mod_wsgi”

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Advanced Django Form Usage @pydanny / @maraujop views.py 43 from django.forms.models import formset_factory def wsgi_form_view(request): WsgiFormset = formset_factory(ExampleForm, extra=5, formset=ItemFormSet) formset = WsgiFormset(bogus_number, request.POST, request.FILES) Truncated formset view

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Lets do programmatic layout of forms

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Advanced Django Form Usage @pydanny / @maraujop Things I want python to describe in forms • Diﬀerent ﬁeldsets within the same form • Various buttons • submit • reset 45

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Advanced Django Form Usage @pydanny / @maraujop django-uni-form 46

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Advanced Django Form Usage @pydanny / @maraujop Programmatic layouts 47 class ExampleForm(forms.Form): def __init__(self, *args, **kwargs): self.helper = FormHelper() self.helper.layout = Layout( Fieldset( 'first arg is the legend of the fieldset', 'like_website', 'favorite_number', ), Fieldset( 'second arg is the legend of the fieldset', 'favorite_color', 'favorite_food', ) ButtonHolder( Submit('submit', 'Submit', css_class='button white') ) ) return super(ExampleForm, self).__init__(*args, **kwargs) from uni_form.helpers import FormHelper, Submit, Reset from uni_form.helpers import Fieldset, ButtonHolder, Layout Fieldset Button Holder Button Layout FormHelper

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Advanced Django Form Usage @pydanny / @maraujop renders as divs 48 {% load uni_form_tags %} {% uni_form my_form my_form.helper %} Renders the HTML form with buttons and everything wrapped in a ﬁeldset.

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Advanced Django Form Usage @pydanny / @maraujop Sample output 49

Name

Comment

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Advanced Django Form Usage @pydanny / @maraujop django-uni-form • Programmatic layout • Div based forms • Section 508 compliant • Fully customizable templates • http://django-uni-form.rtfd.org 50

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What about HTML5 Fields?

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Advanced Django Form Usage @pydanny / @maraujop django-ﬂoppyforms • by Bruno Renie @brutasse • HTML5 Widgets • Fully customizable templates • Plays nice with django-uni-form 52

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Advanced Django Form Usage @pydanny / @maraujop Easy to use! • Django’s widget parameter attrs expects a dictionary • Replaces the normal widgets with HTML5 ones 53 import ﬂoppyforms as forms class ExampleForm(forms.Form): username = forms.CharField( label='', widget = forms.TextInput( attrs={'placeholder': '@johndoe'}, ), )

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Advanced Django Form Usage @pydanny / @maraujop Customizable widgets 54 import floppyforms as forms class OtherEmailInput(forms.EmailInput): template_name = 'path/to/other_email.html' path/to/other_email.html forms.py

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Can you combine django-uni-form and django-ﬂoppyforms?

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django-uni-form + django-ﬂoppyforms AWESOME POWER =

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Advanced Django Form Usage @pydanny / @maraujop They get along well 57 class ListFriendsForm(forms.Form): username = forms.CharField( widget = forms.TextInput( attrs={'placeholder': '@maraujop'}, ), ) def __init__(self, *args, **kwargs): self.helper = FormHelper() self.helper.layout = Layout( Div( 'username', ) ButtonHolder( Submit('submit', 'Submit', css_class='button white') ) ) return super(ExampleForm, self).__init__(*args, **kwargs) No changes or special code needed

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Forms refactor Django 1.4

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Advanced Django Form Usage @pydanny / @maraujop What we are getting in 1.4 • Form rendering will use templates instead of HTML in Python • Template based widgets • Template based form layout 59

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Advanced Django Form Usage @pydanny / @maraujop forms refactor and django-uni-form • forms refactor layout “lives” in templates • django-uni-form layout “lives” in python • Diﬀerent approaches, same objective 60

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Give me a way to create custom form ﬁelds

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Advanced Django Form Usage @pydanny / @maraujop The docs on custom ﬁelds 62 “Its only requirements are that it implement a clean() method and that its __init__() method accept the core arguments mentioned above (required, label, initial, widget, help_text).” The docs seem to be wrong

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Advanced Django Form Usage @pydanny / @maraujop How it really works • required • widget • label • help_text • initial • error_messages • show_hidden_initial • validators • localize 63 You don’t need to implement “clean” You do need to implement:

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How the heck then do I actually add a custom form ﬁeld?!?

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Advanced Django Form Usage @pydanny / @maraujop How does form validation work? 65

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Advanced Django Form Usage @pydanny / @maraujop ﬁelds.py 66 class AMarkField(forms.Field): widget = TextInput default_error_messages = { 'not_an_a': _(u'you can only input A here! damn!'), } def __init__(self, **kwargs): super(AMarkField, self).__init__(**kwargs) def to_python(self, value): if value in validators.EMPTY_VALUES: return None if value != 'A': raise ValidationError(self.error_messages['not_an_a']) return value Only accepts upper case A as input

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Advanced Django Form Usage @pydanny / @maraujop Not DRY 67 class MyModelForm(forms.ModelForm): mark = CharField() def clean_mark(self): mark_value = self.cleaned_data['mark'] if mark_value is not None or mark_value.upper() != 'A': raise ValidationError(_(u'Only input A here!')) return mark_value class ExampleForm(forms.Form): mark = CharField() def clean_mark(self): mark_value = self.cleaned_data['mark'] if mark_value is not None or mark_value.upper() != 'A': raise ValidationError(_(u'Only input A here!')) return mark_value

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I want a custom ﬁeld that validates JSON

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Advanced Django Form Usage @pydanny / @maraujop The JSON ﬁeld 69 class JSONField(forms.Field): default_error_messages = { 'invalid': 'This is not valid JSON string' } def to_python(self, value): if value in validators.EMPTY_VALUES: return None try: json = simplejson.loads(value) except ValueError: raise ValidationError(self.error_messages['invalid']) return json

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I want a custom widget that handles multiple widgets

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Advanced Django Form Usage @pydanny / @maraujop widgets.py 71 from django.forms.extras.widgets import MultiWidget class AddressWidget(MultiWidget): def __init__(self, attrs=None): widgets = (TextInput, TextInput) super(AddressWidget, self).__init__(widgets, attrs) def decompress(self, value): """ If called, value is a string should return a list """ if value: # parse stuff and return a list return value.split() return [None, None] Called when a form with MultiWidget is passed initial or instance values Two TextInput widgets!!!

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Advanced Django Form Usage @pydanny / @maraujop ﬁelds.py 72 class AddressField(forms.Field): self.widget = AddressWidget def to_python(self, value): # Already gets a Python list return value isinstance(["921 SW Sixth Avenue", "Portland"], list) class ExampleForm(object): forms.CharField(widget=AddressWidget) isinstance("921 SW Sixth Avenue, Portland", str)

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Give me a MultiValue, MultiWidget ﬁeld

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Advanced Django Form Usage @pydanny / @maraujop MultiValue, MultiWidget Field • Clean does not work in the standard way • Every ﬁeld validated with its corresponding widget value • Beware! run_validator does run but validate is called 74 class AlternativeAddressField(forms.MultiValueField): widget = AddressWidget def __init__(self, *args, **kwargs): fields = (forms.CharField(), forms.CharField()) super(AlternativeAddressField, self).__init__(fields, *args, **kwargs) def compress(self, data_list): return data_list Django Ticket #14184

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Advanced Django Form Usage @pydanny / @maraujop Validators with Multi-Field 75 class AlternativeAddressField(forms.MultiValueField): widget = AddressWidget def __init__(self, *args, **kwargs): fields = (forms.CharField(), forms.CharField()) super(AlternativeAddressField, self).__init__(fields, *args, **kwargs) def validate(self, value): self._run_validators(value) def compress(self, data_list): return data_list

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How about custom widget output?

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Advanced Django Form Usage @pydanny / @maraujop def render(self, name, value, attrs=None): # HTML to be added to the output widget_labels = [ 'Address: ', 'Number: ' ] if self.is_localized: for widget in self.widgets: widget.is_localized = self.is_localized # value is a list of values, each corresponding to a widget # in self.widgets. if not isinstance(value, list): value = self.decompress(value) output = [] final_attrs = self.build_attrs(attrs) id_ = final_attrs.get('id', None) for i, widget in enumerate(self.widgets): try: widget_value = value[i] except IndexError: widget_value = None if id_: final_attrs = dict(final_attrs, id='%s_%s' % (id_, i)) # Adding labels output.append(widget_labels[i] % ('%s_%s' % (name, i))) output.append(widget.render(name + '_%s' % i, widget_value, final_attrs)) return mark_safe(self.format_output(output)) Custom Widget Output 77 So Easy!

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Can’t you make it easier to understand?

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Advanced Django Form Usage @pydanny / @maraujop Problems with Custom Widget Output • Overring render means indepth knowledge • Hard to do custom output with built-in widgets • You can’t call super.render and customize easily • Templates? Open Ticket #15667 79

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Not in Lawrence Kansas anymore

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Advanced Django Form Usage @pydanny / @maraujop Problems with Custom Widget Output • Oldest ticket in Django is related to forms (#23) • ComboField is broken • Validators are thought to validate simple values because of the way run_validators is coded 81

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Advanced Django Form Usage @pydanny / @maraujop HTML5 tickets • Ticket #16304 • Ticket #16630 • Just use django-ﬂoppyforms 82

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Advanced Django Form Usage @pydanny / @maraujop Validators • Imagine you have an input that get a list of emails seperated by spaces • Your widget returns: [“a@example.com”, “b@example.com”] • You want to run validators on all of them • There is an EmailValidator 83

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Advanced Django Form Usage @pydanny / @maraujop MultiValidator 84 class MultiValidator(object): def __init__(self, validators): self.validators = validators def __call__(self, data_list): errors = [] for value in data_list: for validator in self.validators: try: validator(value) except ValidationError, e: if hasattr(e, 'code'): errors.append("FiXED MESSAGE") raise ValidationError(errors)

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Advanced Django Form Usage @pydanny / @maraujop Amazing stuff • Ticket #27 reported by Adrian Holovaty • Single form field for multiple database fields 85

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Fin

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Advanced Django Form Usage @pydanny / @maraujop This has been incredible • We’ve just scratched the surface • Keep your code clean - or you’ll regret it • Miguel is awesome 87

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Advanced Django Form Usage @pydanny / @maraujop This has been incredible • We want to see this and more in the formal Django docs • We’ve scratched our own itch • There are hidden things that need to see the light of day • Danny holds the DjangoCon talks record 88

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Fin

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Advanced Django Form Usage @pydanny / @maraujop Questions? 90 Daniel Greenfeld & Miguel Araujo