Christine Spang: Django form fields with the same name as Python keywords

Fri, 04 Jun 2010 00:58:11 +0000

For work recently I've been doing some Django-related tasks that involve talking to an external API with POSTed forms. Django forms objects are declared by creating a class that inherits from django.forms.Form, with the fields of the form declared by declaring attributes of that class. Which works well and is clean and easy to remember—unless the API you're working with requires a field with the same name as a Python keyword, such as return. You can't declare a field like this as an attribute; it will trigger a syntax error.

I spent some time scratching my head over this, and came up with this as a workaround after source-diving to find out how Form objects actually work:

from django import forms

class ExampleForm(forms.Form):
    def __init__(self, data=None, files=None, auto_id='id_%s', prefix=None,
            initial=None, errorclass=ErrorList, label_suffix=':', empty_permitted=False, return_url=None):
        forms.Form.__init__(self, data, files, auto_id, prefix, initial,
            errorclass, label_suffix, empty_permitted)
        if return_url is not None:
            self.fields['return'] = forms.CharField(widget=forms.HiddenInput, initial=return_url)

It turns out that the attribute declaration is just syntactic sugar for creating a dictionary of key/value pairs, which is then stored in the fields attribute. So we can monkeypatch in extra values after the translation. Which is somewhat more awkward and ugly, but works in a pinch.

Note that I haven't extensively tested what interactions this may cause with other forms code, so use with some caution.

tag django

Christine Spang: Django form fields with the same name as Python keywords