Return a 404 error when no dstat csv can be loaded

stackviz/views/dstat/api.py

@@ -1,4 +1,6 @@
-from django.http import HttpResponse
+import os
+
+from django.http import HttpResponse, Http404
 from django.views.generic import View
 
 from stackviz import settings
@@ -12,11 +14,19 @@ def _load_csv():
     if _cached_csv:
         return _cached_csv
 
-    with open(settings.DSTAT_CSV, 'r') as f:
-        _cached_csv = f.readlines()
-        return _cached_csv
+    try:
+        with open(settings.DSTAT_CSV, 'r') as f:
+            _cached_csv = f.readlines()
+            return _cached_csv
+    except IOError:
+        return None
 
 
 class DStatCSVEndpoint(View):
     def get(self, request):
-        return HttpResponse(_load_csv(), content_type="text/csv")
+        csv = _load_csv()
+
+        if not csv:
+            raise Http404("DStat log not loaded.")
+
+        return HttpResponse(csv, content_type="text/csv")