Initial add of On This Day links to svx file page

core/models/survex.py

@@ -1,6 +1,7 @@
 import os
 import re
 from urllib.parse import urljoin
+from pathlib import Path
 
 from django.conf import settings
 from django.db import models
@@ -39,8 +40,8 @@ class SurvexFile(models.Model):
     # return "[SurvexFile:"+str(self.path) + "-" + str(self.survexdirectory) + "-" + str(self.cave)+"]"
 
     def exists(self):
-        fname = os.path.join(settings.SURVEX_DATA, self.path + ".svx")
-        return os.path.isfile(fname)
+        fname = Path(settings.SURVEX_DATA, self.path + ".svx")
+        return fname.is_file()
 
     def OpenFile(self):
         fname = os.path.join(settings.SURVEX_DATA, self.path + ".svx")
@@ -64,6 +65,8 @@ class SurvexFile(models.Model):
 
 
 class SurvexStationLookUpManager(models.Manager):
+    """Don't know what this does, 
+    https://docs.djangoproject.com/en/dev/topics/db/managers/"""
     def lookup(self, name):
         blocknames, sep, stationname = name.rpartition(".")
         return self.get(block=SurvexBlock.objects.lookup(blocknames), name__iexact=stationname)
@@ -99,9 +102,8 @@ class SurvexStation(models.Model):
 # Single SurvexBlock
 #
 class SurvexBlockLookUpManager(models.Manager):
-    """Don't know what this does, suspect it is part of the Django admin
-    system"""
-
+    """Don't know what this does,  
+    https://docs.djangoproject.com/en/dev/topics/db/managers/ """
     def lookup(self, name):
         if name == "":
             blocknames = []