Passing an empty QueryDict to a form stores it as a plain dictionary

[Stefan Wehrmeyer]

Passing an empty request.POST or request.FILES into a form, evaluates the arguments to False ​in these lines and stores a normal Python dictionary instead.

self.data = data or {}
self.files = files or {}

This breaks the assumption that what you pass into the form will be kept allowing access to special methods like QueryDict.getlist.

The following code accepts zero or more uploaded files, but breaks when no files are uploaded because the passed QueryDict gets discarded and a dict has no method getlist.

class UploadForm(forms.Form):
    documents = forms.FileField(
        required=False,
        widget=forms.FileInput(attrs={
          'multiple': True
        })
    )

    def save(self):
        for doc in self.files.getlist('documents'):
            handle_doc(doc)


form = UploadForm(request.POST, request.FILES)
form.save()

# When request.FILES is empty
# AttributeError: 'dict' object has no attribute 'getlist'

Instead of

self.data = data or {}
self.files = files or {}

it should be something like

self.data = QueryDict() if data is None else data
self.files = QueryDict() if files is None else files

which would keep whatever was passed except None and fall back to an empty QueryDict instance which is the type of the usual parameter.

The only backwards incompatible change here would be that self.data and self.files are no longer mutable as they would be when set to empty dicts, but afaik the attributes are not changed anyway.

[Stefan Wehrmeyer]

​Pull Request

[Abhishek Gautam]

I am working on this.

[Tim Graham <timograham@…>]

In 1aa8e860:

Fixed #27989 -- Preserved empty QueryDicts for form's data/files args.