Merge pull request #3260 from LBWright/error-handling

adds api error handling example to documentation

docs/patterns/errorpages.rst

@@ -97,3 +97,29 @@ An example template might be this:
       <p>What you were looking for is just not there.
       <p><a href="{{ url_for('index') }}">go somewhere nice</a>
     {% endblock %}
+
+
+Returning API errors as JSON
+----------------------------
+
+When using Flask for web APIs, you can use the same techniques as above
+to return JSON responses to API errors.  :func:`~flask.abort` is called
+with a ``description`` parameter. The :meth:`~flask.errorhandler` will
+use that as the JSON error message, and set the status code to 404.
+
+.. code-block:: python
+
+    from flask import abort, jsonify
+
+    @app.errorhandler(404)
+    def resource_not_found(e):
+        return jsonify(error=str(e)), 404
+
+    @app.route("/cheese")
+    def get_one_cheese():
+        resource = get_resource()
+
+        if resource is None:
+            abort(404, description="Resource not found")
+
+        return jsonify(resource)