First attempts to use type hinting

app/email.py

@@ -1,17 +1,25 @@
 from flask import current_app, render_template
 from flask_mail import Message
+from typing import Any, Text
 from . import mail
 from .decorators import background
 
 
-def create_message(recipient, subject, template, **kwargs):
-    msg = Message('{} {}'.format(current_app.config['NOPAQUE_MAIL_SUBJECT_PREFIX'], subject), recipients=[recipient])  # noqa
-    msg.body = render_template('{}.txt.j2'.format(template), **kwargs)
-    msg.html = render_template('{}.html.j2'.format(template), **kwargs)
+def create_message(
+    recipient: str,
+    subject: str,
+    template: str,
+    **kwargs: Any
+) -> Message:
+    subject_prefix: str = current_app.config['NOPAQUE_MAIL_SUBJECT_PREFIX']
+    msg: Message = Message(
+        f'{subject_prefix} {subject}', recipients=[recipient])
+    msg.body: Text = render_template(f'{template}.txt.j2', **kwargs)
+    msg.html: Text = render_template(f'{template}.html.j2', **kwargs)
     return msg
 
 
 @background
-def send(msg, *args, **kwargs):
+def send(msg: Message, *args, **kwargs):
     with kwargs['app'].app_context():
         mail.send(msg)