Django AuthenticationForm gotchas —03 December 2010

If you initialize as AuthentictionForm(request.POST) like probably many of your forms, no validation will take place at all.

In my case I needed to initialize as AuthenticationForm(None, request.POST)

The gotcha here is that the first argument must be a request object if you want to validate cookie support in the browser (that is, check if the user has cookies enabled in the browser). I didn’t want cookie validation, but I did want field and user account validation.

Another gotcha was handling the ‘invalid username-password error’. Field validation errors are linked to a field, so a missing username error is stored in form.username.errors. But the invalid username-password error is not specific to one field. You can find these errors in form.non_field_errors, but this is hard to find in the documentation. Also, the error messages are already formatted. I don’t know why they did it that way. Instead of a list of error messages, they made this one a <ul> formatted html.