Author: John Au-Yeung

To fix the Python Django MultiValueDictKeyError error, we use the dictionary get method to get the dict value and return a default if the dict key doesn’t exist.

For instance, we write

is_private = request.POST.get('is_private', False)

to call get on request.POST to get the is_private dict value from the POST request payload.

And if is_private wasn’t sent, then we return False.

To handle multiple forms on one page in Python Django, we can set the forms to use in our views.

For instance, we write

if request.method == 'POST':
    bannedphraseform = BannedPhraseForm(request.POST, prefix='banned')
    if bannedphraseform.is_valid():
        bannedphraseform.save()
else:
    bannedphraseform = BannedPhraseForm(prefix='banned')

if request.method == 'POST' and not bannedphraseform.is_valid():
    expectedphraseform = ExpectedPhraseForm(request.POST, prefix='expected')
    bannedphraseform = BannedPhraseForm(prefix='banned')
    if expectedphraseform.is_valid():
        expectedphraseform.save()

else:
    expectedphraseform = ExpectedPhraseForm(prefix='expected')

in our view to set different forms to use according to different conditions.

We use if statements to check request methods and form validation to assign which form to render in the page.

To filter ForeignKey choices in a Python Django ModelForm, we set the quertset property to the queryset with the filtered data.

For instance, we write

class ClientAdminForm(forms.ModelForm):
    def __init__(self, *args, **kwargs):
        super(ClientAdminForm, self).__init__(*args, **kwargs)
        # access object through self.instance...
        self.fields['base_rate'].queryset = Rate.objects.filter(company=self.instance.company)

class ClientAdmin(admin.ModelAdmin):
    form = ClientAdminForm

to add the ClientAdminForm that sets the base_rate field’s queryset to the filtered Rate query set with

Rate.objects.filter(company=self.instance.company)

Then we add the ClientAdminForm form as the form to use in the ClientAdmin section of Django admin.

To capture URL parameters in request.GET with Python Django, we can add a view to match a URL pattern that takes a URL parameter.

Then we can get the parameter value from the view function’s parameter.

For instance, we write

(r'^user/(?P<username>\w{0,50})/$', views.profile_page,),

to add a view that matches the r'^user/(?P<username>\w{0,50})/$' route.

Then in our view file, we add a view with

def profile_page(request, username):
    # ...

to get the username URL parameter value from username.

To make Python Django serve downloadable files, we can return a response with some special values.

For instance, we write

from django.utils.encoding import smart_str

response = HttpResponse(content_type='application/force-download')
response['Content-Disposition'] = 'attachment; filename=%s' % smart_str(file_name)
response['X-Sendfile'] = smart_str(path_to_file)
return response

to create a HttpResponse instance and assign it to response.

Then we set the Content-Disposition response header with

response['Content-Disposition'] = 'attachment; filename=%s' % smart_str(file_name)

And then we set the X-Sendfile header to the path of the file with

response['X-Sendfile'] = smart_str(path_to_file)

And then we return the response in our view.