Fix

web/app/settings/tasks.py

@@ -0,0 +1,13 @@
+from .. import db
+from ..decorators import background
+from ..models import User
+
+
+@background
+def delete_user(user_id, *args, **kwargs):
+    with kwargs['app'].app_context():
+        user = User.query.get(user_id)
+        if user is None:
+            raise Exception('User {} not found'.format(user_id))
+        user.delete()
+        db.session.commit()

web/app/settings/views.py

@@ -1,6 +1,6 @@
 from flask import current_app, flash, redirect, render_template, url_for
 from flask_login import current_user, login_required
-from . import settings
+from . import settings, tasks
 from .forms import (ChangePasswordForm, EditGeneralSettingsForm,
                     EditNotificationSettingsForm)
 from .. import db