Refactor: separate forms from view, improve code style

src/pretix/control/forms/organizer.py

@@ -0,0 +1,33 @@
+from django import forms
+from django.utils.translation import ugettext_lazy as _
+from pretix.base.forms import VersionedModelForm
+
+from pretix.base.models import Organizer
+
+
+class OrganizerForm(VersionedModelForm):
+    error_messages = {
+        'duplicate_slug': _("This slug is already in use. Please choose a different one."),
+    }
+
+    class Meta:
+        model = Organizer
+        fields = ['name', 'slug']
+
+    def clean_slug(self):
+        slug = self.cleaned_data['slug']
+        if Organizer.objects.filter(slug=slug).exists():
+            raise forms.ValidationError(
+                self.error_messages['duplicate_slug'],
+                code='duplicate_slug',
+            )
+        return slug
+
+
+class OrganizerUpdateForm(OrganizerForm):
+    def __init__(self, *args, **kwargs):
+        super().__init__(*args, **kwargs)
+        self.fields['slug'].widget.attrs['disabled'] = 'disabled'
+
+    def clean_slug(self):
+        return self.instance.slug