Pass parameter to Form in Django - 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 ?

Answer 1

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.

Answer 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

Answer 3

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?

Answer 4

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.

Answer 5

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