<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def get_success_url(self):
 """Return the URL to redirect to after processing a valid form."""

        if not self.success_url:
            if self.request.GET.get("inmodal"):
                return reverse("arctic:redirect_to_parent")
            raise ImproperlyConfigured(
                "No URL to redirect to. Provide a success_url."
            )
        return self.in_modal(str(self.success_url))