core/sources(minor): refactor Source's property

passbook/core/models.py

@@ -152,14 +152,10 @@ class Source(PolicyModel):
     objects = InheritanceManager()
 
     @property
-    def is_link(self):
-        """Return true if Source should get a link on the login page"""
-        return False
-
-    @property
-    def get_login_button(self):
-        """Return a tuple of URL, Icon name and Name"""
-        raise NotImplementedError
+    def login_button(self):
+        """Return a tuple of URL, Icon name and Name
+        if Source should get a link on the login page"""
+        return None
 
     @property
     def additional_info(self):

passbook/core/views/authentication.py

@@ -46,9 +46,11 @@ class LoginView(UserPassesTestMixin, FormView):
         kwargs['show_sign_up_notice'] = CONFIG.y('passbook.sign_up.enabled')
         kwargs['sources'] = []
         sources = Source.objects.filter(enabled=True).select_subclasses()
-        if any(source.is_link for source in sources):
-            for source in sources:
-                kwargs['sources'].append(source.get_login_button)
+        for source in sources:
+            login_button = source.login_button
+            if login_button:
+                kwargs['sources'].append(login_button)
+        if kwargs['sources']:
             self.template_name = 'login/with_sources.html'
         return super().get_context_data(**kwargs)