fix: allow caller to specify default subject for email message

we already allow for some config fallbacks but sometimes the caller
needs to declare the default, to use as fallback when specific config
is not present

src/wuttjamaican/email.py

@@ -370,7 +370,7 @@ class EmailHandler(GenericHandler):
         """
         return Message(**kwargs)
 
-    def make_auto_message(self, key, context={}, **kwargs):
+    def make_auto_message(self, key, context={}, default_subject=None, **kwargs):
         """
         Make a new email message using config to determine its
         properties, and auto-generating body from a template.
@@ -386,6 +386,9 @@ class EmailHandler(GenericHandler):
         :param context: Context dict used to render template(s) for
            the message.
 
+        :param default_subject: Optional :attr:`~Message.subject`
+           template/string to use, if config does not specify one.
+
         :param \**kwargs: Any remaining kwargs are passed as-is to
            :meth:`make_message()`.  More on this below.
 
@@ -408,7 +411,7 @@ class EmailHandler(GenericHandler):
         if 'sender' not in kwargs:
             kwargs['sender'] = self.get_auto_sender(key)
         if 'subject' not in kwargs:
-            kwargs['subject'] = self.get_auto_subject(key, context)
+            kwargs['subject'] = self.get_auto_subject(key, context, default=default_subject)
         if 'to' not in kwargs:
             kwargs['to'] = self.get_auto_to(key)
         if 'cc' not in kwargs:
@@ -449,7 +452,7 @@ class EmailHandler(GenericHandler):
         # fall back to global default, if present
         return self.config.get(f'{self.config.appname}.email.default.replyto')
 
-    def get_auto_subject(self, key, context={}, rendered=True, setting=None):
+    def get_auto_subject(self, key, context={}, rendered=True, setting=None, default=None):
         """
         Returns automatic :attr:`~wuttjamaican.email.Message.subject`
         line for a message, as determined by config.
@@ -470,15 +473,17 @@ class EmailHandler(GenericHandler):
            instance.  This is passed along to
            :meth:`get_auto_subject_template()`.
 
+        :param default: Default subject to use if none is configured.
+
         :returns: Final subject text, either "raw" or rendered.
         """
-        template = self.get_auto_subject_template(key, setting=setting)
+        template = self.get_auto_subject_template(key, setting=setting, default=default)
         if not rendered:
             return template
 
         return Template(template).render(**context)
 
-    def get_auto_subject_template(self, key, setting=None):
+    def get_auto_subject_template(self, key, setting=None, default=None):
         """
         Returns the template string to use for automatic subject line
         of a message, as determined by config.
@@ -497,6 +502,8 @@ class EmailHandler(GenericHandler):
            optimization; otherwise it will be fetched if needed via
            :meth:`get_email_setting()`.
 
+        :param default: Default subject to use if none is configured.
+
         :returns: Final subject template, as raw text.
         """
         # prefer configured subject specific to key
@@ -504,6 +511,10 @@ class EmailHandler(GenericHandler):
         if template:
             return template
 
+        # or use caller-specified default, if applicable
+        if default:
+            return default
+
         # or subject from email setting, if defined
         if not setting:
             setting = self.get_email_setting(key)

tests/test_email.py

@@ -291,7 +291,7 @@ class TestEmailHandler(ConfigTestCase):
             msg = handler.make_auto_message('foo', subject=None)
             get_auto_subject.assert_not_called()
             msg = handler.make_auto_message('foo')
-            get_auto_subject.assert_called_once_with('foo', {})
+            get_auto_subject.assert_called_once_with('foo', {}, default=None)
 
         # to
         with patch.object(handler, 'get_auto_to') as get_auto_to:
@@ -376,7 +376,7 @@ class TestEmailHandler(ConfigTestCase):
         template = handler.get_auto_subject_template('foo')
         self.assertEqual(template, "Foo Message")
 
-        # setting can provide default subject
+        # EmailSetting can provide default subject
         providers = {
             'wuttatest': MagicMock(email_modules=['tests.test_email']),
         }
@@ -385,6 +385,10 @@ class TestEmailHandler(ConfigTestCase):
             template = handler.get_auto_subject_template('mock_foo')
             self.assertEqual(template, "MOCK FOO!")
 
+            # caller can provide default subject
+            template = handler.get_auto_subject_template('mock_foo', default="whatever is clever")
+            self.assertEqual(template, "whatever is clever")
+
     def test_get_auto_subject(self):
         handler = self.make_handler()
 
@@ -397,6 +401,10 @@ class TestEmailHandler(ConfigTestCase):
         subject = handler.get_auto_subject('foo')
         self.assertEqual(subject, "Wutta Message")
 
+        # caller can provide default subject
+        subject = handler.get_auto_subject('foo', default="whatever is clever")
+        self.assertEqual(subject, "whatever is clever")
+
         # can configure just for key
         self.config.setdefault('wutta.email.foo.subject', "Foo Message")
         subject = handler.get_auto_subject('foo')