rename: Add valid fields to --help

bin/rename

@@ -24,6 +24,7 @@ fInbox=False
 files=[]
 commitDir=None
 setFields=dict()
+validFields= [ "lecture", "examiner", "examType" ]
 
 for cmd in pdfViewersAll:
   if shutil.which(cmd)!=None:
@@ -98,14 +99,15 @@ def print_help(f):
     "  -s|--set-field <field> <item>\n"
     "    Provide a default for a specific field that is used in every \n"
     "    renaming. If it is an exam type, it overrides anything that might \n"
-    "    already be there.\n"
+    "    already be there. Valid fields are: {valFields}\n"
     "environment variables: \n"
     "  KA_PDF_VIEWER\n"
     "    executable name of the preferred pdf viewer. This serves as the \n"
     "    default for --pdf-viewer. \n"
     "".format(
         pdfViewer=pdfViewer,
-      pdfViewers="|".join(sorted(pdfViewers))
+        pdfViewers="|".join(sorted(pdfViewers)),
+        valFields=", ".join(validFields)
       )
     )
 
@@ -137,7 +139,7 @@ try:
       s=None
     elif s=="--set-field":
       field_name=arg
-      if not arg in { "lecture", "examiner", "examType" }: 
+      if not arg in validFields: 
         raise CLEx("Invalid field name: %s"%arg)
       s="--set-field:1"
     elif s=="--set-field:1":