automatically determine number of custom questions

export.py

@@ -61,18 +61,18 @@ class Signup:
 def process(reader: csv.reader) -> Dict[str, List[Signup]]:
     event_data = collections.defaultdict(list)
     all_by_mail = collections.defaultdict(list)
+    number_of_custom_questions = sum(
+            1 for fieldname in reader.fieldnames if fieldname.startswith('Question ')
+    )
 
     for linenum, line in enumerate(reader):
         date, slot = line['Start Date & Time'].split(' ')
         assert date == DATE, date
 
         exams = []
-        for i in range(1, 5):
+        for i in range(1, number_of_custom_questions + 1):
             key = f'Response {i}'
-            if key in line:
-                exams += line[key].split('\n')
-            elif linenum == 1:
-                print(f"!!! No {key} key in export!")
+            exams += line[key].split('\n')
         exams = [e for e in exams if e]
 
         lastname = line['Invitee Last Name']