Turn short_name into identifier and force it to be a Python identifier. Advances #45.

biscuit/apps/alsijil/models.py

@@ -47,11 +47,12 @@ class LessonDocumentation(SchoolRelated):
 class PersonalNoteFilter(SchoolRelated):
     """ A filter definition that can generate statistics on personal note texts. """
 
-    short_name = models.CharField(verbose_name=_('Short name'), max_length=30)
+    identifier = models.CharField(verbose_name=_('Identifier'), max_length=30,
+                                  validators=[lambda v: v.isidentifier()])
     description = models.CharField(verbose_name=_('Description'), max_length=60, blank=True)
 
     regex = models.CharField(verbose_name=_('Match expression'), max_length=100)
 
     class Meta:
-        unique_together = [['school', 'short_name'], ['school', 'description'], ['school', 'regex']]
+        unique_together = [['school', 'identifier'], ['school', 'description'], ['school', 'regex']]
         ordering = ['short_name']