How to pass text argument to custom widget in django form? - django

Question

I'd like to display a dynamic text value in a custom widget.
It will more or less be a bootstrap input group with some dynamic text in a input-group-append element.
I'm having difficulty understanding how I can pass this through to the template, as when I define the field in the Form class, I can't seem to reference arguments from the Form constructor.
I'm inexperienced with both python and django so its very likely I'm missing some foundational python knowledge that's causing my confusion.
If I do this, the widget renders partially ok (There is an automatic label "Site prefix" rendered that I don't want but that seems like a different problem)
class SiteNameForm(forms.Form):
site_prefix = forms.CharField(widget=SiteNameInputWidget(prefix_for='T E S T'), label=None)
And create the form like so
form = SiteNameForm()
However, I need to pass in a dynamic value, so I tried
class SiteNameForm(forms.Form):
def __init__(self, prefix_for=None, *args, **kwargs):
self.prefix_for = prefix_for
self.site_prefix = forms.CharField(widget=SiteNameInputWidget(prefix_for=self.prefix_for))
super().__init__(self, args, kwargs)
While creating the form
form = SiteNameForm(prefix_for='TEST')
But when I do that, nothing is rendered at all, not even the automatic label that I didn't want.
The template specified as template_name
<div class="row">
<div class="input-group mb-3">
<div class="input-group-prepend">
<span class="input-group-text">https://</span>
</div>
<input type="text" id="site_prefix" name="site_prefix" class="form-control" aria-label="prefix">
<div class="input-group-append">
<span class="input-group-text">.<span class="domain-suffix-type">{{ prefix_for }}</span>.foo.bar</span>
</div>
</div>
Is there a way to accomplish what I'm trying to do?