add helpers for making API parameters required

zesje/resources/_helpers.py

+
+def nonempty_string(s):
+    s = str(s)
+    if not s:
+        raise ValueError('cannot be an empty string')
+    return s
+
+def required_string(parser, name):
+    parser.add_argument(name, type=nonempty_string,
+                        required=True, nullable=False)

zesje/resources/exams.py

@@ -7,9 +7,9 @@ from werkzeug.datastructures import FileStorage
 
 from pony import orm
 
-from ..helpers import yaml_helper
+from ..helpers import yaml_helper, db_helper
 from ..models import db, Exam, Problem, FeedbackOption
-from ..helpers import db_helper
+from ._helpers import required_string
 
 
 class ExamConfig(Resource):
@@ -31,11 +31,12 @@ class ExamConfig(Resource):
             'yaml': yml
         }
 
+    patch_parser = reqparse.RequestParser()
+    required_string(patch_parser, 'yaml')
+
     @orm.db_session
     def patch(self, id):
-        parser = reqparse.RequestParser()
-        parser.add_argument('yaml', type=str, required=True)
-        args = parser.parse_args()
+        args = patch_parser.parse_args()
 
         exam = Exam[id]
 

zesje/resources/graders.py

@@ -6,15 +6,12 @@ from flask_restful import Resource, reqparse
 from pony import orm
 
 from ..models import db, Grader
+from ._helpers import required_string
+
 
-parser = reqparse.RequestParser()
-parser.add_argument('first_name', type=str, required=True)
-parser.add_argument('last_name', type=str, required=True)
 # TODO: when making new database structure, have only a single
 #       'name' field: it is just an identifier
 
-
-
 class Graders(Resource):
     """ Graders that are able to use the software, also logged during grading """
 
@@ -42,6 +39,10 @@ class Graders(Resource):
             for g in Grader.select()
         ]
 
+    post_parser = reqparse.RequestParser()
+    required_string(post_parser, 'first_name')
+    required_string(post_parser, 'last_name')
+
     @orm.db_session
     def post(self):
         """add a grader.
@@ -58,15 +59,13 @@ class Graders(Resource):
             first_name: str
             last_name: str
         """
-
-        args = parser.parse_args()
-
+        args = post_parser.parse_args()
         
         try:
             Grader(first_name= args['first_name'],
-                        last_name=args['last_name'])
+                   last_name=args['last_name'])
             orm.commit()
-        except KeyError as _e:
-            abort(400, _e)
+        except KeyError as error:
+            abort(400, error)
 
         return self._get()