Pass parameter to Form in Django

Question

I have a custom form to which I would like to pass a parameter. Following this example I came up with the following code :

class EpisodeCreateForm(forms.Form):
    def __init__(self, *args, **kwargs):
        my_arg = kwargs.pop('my_arg')
        super(EpisodeCreateForm, self).__init__(*args, **kwargs)

    my_field = forms.CharField(initial=my_arg)

But I get the following error:

Exception Value: name 'my_arg' is not defined

How can I get it to recognize the argument in the code of the form ?

sandinmyjoints · Accepted Answer · 2011-08-31 15:23:16Z

8

You need to set the initial value by referring to the form field instance in __init__. To get access to the form field instance in __init__, put this before the call to super:

self.fields['my_field'].initial=my_arg

And remove initial=my_arg from where you declare my_field because at that point (when class is declared) my_arg is not in scope.

answered Aug 31, 2011 at 15:23

sandinmyjoints

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4 Comments

Johanna Over a year ago

it doesn't know the attributes fields, is that normal ? And what if I want to later use this argument in the save method of the form ?

sandinmyjoints Over a year ago

I goofed--the call to super needs to come before self.fields or else it won't exist yet.

Johanna Over a year ago

Cool, this works ! And what if I want to use this varaible in the save method of the form ?

Johanna Over a year ago

Well I guess I can pass it in a hidden field like this. It work. ANy way thanks :)

Maxime Lorant · Accepted Answer · 2015-04-28 12:35:14Z

2

The thing is that my_field is initialized when the class is created, but my_arg is initialized when a new instance is created, far too late for my_field to know its value. What you can do is initialize my_field in __init__ too:

def __init__(self, *args, **kwargs):
    my_arg = kwargs.pop('my_arg')
    super(EpisodeCreateForm, self).__init__(*args, **kwargs)
    if not self.my_field:
        self.my_field = my_arg

edited Apr 28, 2015 at 12:35

Maxime Lorant

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answered Aug 31, 2011 at 14:59

Gabi Purcaru

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3 Comments

Johanna Over a year ago

if I replace my_arg with self.my_arg in both places it appears, then it tells me it doesn't know self..

Johanna Over a year ago

I can't get it to intialize the field in the init method. if I declare the form field in the init method, it juste doesn't show up.

Gabi Purcaru Over a year ago

@Johanna do it after the super(...) function call

Mikhail Korobov · Accepted Answer · 2011-08-31 15:04:08Z

0

This code is executed once at import time:

my_field = forms.CharField(initial=my_arg)

and this code is executed on form instance creation:

my_arg = kwargs.pop('my_arg')
super(EpisodeCreateForm, self).__init__(*args, **kwargs)

So this won't work this way. You should set initial value for the field in your __init__ method.

By the way, all this seems unnecessary, why don't use 'initial' keyword in a view?

answered Aug 31, 2011 at 15:04

Mikhail Korobov

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1 Comment

Johanna Over a year ago

How would you use the initial keyword in a view ?

Daniel Hepper · Accepted Answer · 2011-08-31 16:08:52Z

0

Considering your comment, I would do this:

class EpisodeCreateForm(forms.Form):
    def __init__(self, *args, **kwargs):
        self.my_arg = kwargs.pop('my_arg')
        kwargs.setdefault('initial', {})['my_field'] = self.my_arg
        super(EpisodeCreateForm, self).__init__(*args, **kwargs)

    def save(self):
        do_something(self.my_arg)
        ...
        super(EpisodeCreateForm, self).save()

    my_field = forms.CharField()

Passing initial to the superclass and letting it do the work seems cleaner to me than directly setting it on the field instance.

edited Aug 31, 2011 at 16:08

answered Aug 31, 2011 at 15:22

Daniel Hepper

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1 Comment

Johanna Over a year ago

the value I want to put as initial comes from the view calling the form, that's why I want to pass it as a parameter. And actually I don't just want to use it as an initial value but to perform a sql query in the save method

Edouard Thiel · Accepted Answer · 2015-05-06 15:22:01Z

You simply need to pop your arg before super() and put it in the fields dictionnary after super() :

class EpisodeCreateForm(forms.Form):

    my_field = forms.CharField(label='My field:')

    def __init__(self, *args, **kwargs):
        my_arg = kwargs.pop('my_arg')
        super(EpisodeCreateForm, self).__init__(*args, **kwargs)
        self.fields['my_arg'].initial = my_arg

Then, simply call

form = EpisodeCreateForm (my_arg=foo)

As an example, say you have a table of Episodes, and you want to show the availables ones in a choices menu, and select the current episode. For that, use a ModelChoiceField:

class EpisodeCreateForm(forms.Form):

    available_episode_list = Episode.objects.filter(available=True)

    my_field = forms.ModelChoiceField(label='My field:',
        queryset=available_episode_list)

    def __init__(self, *args, **kwargs):
        cur_ep = kwargs.pop('current_episode')
        super(EpisodeCreateForm, self).__init__(*args, **kwargs)
        self.fields['current_episode'].initial = cur_ep

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