Simplify duration string function.

core/utils.py

@@ -6,25 +6,18 @@ from math import floor
 
 def duration_string(start, end):
     diff = end - start
-    if diff.seconds < 60:
-        duration = '{} second{}'.format(
-            diff.seconds,
-            's' if diff.seconds > 1 else ''
-        )
-    elif diff.seconds < 3600:
-        duration = '{} minute{}, {} second{}'.format(
-            floor(diff.seconds / 60),
-            's' if floor(diff.seconds / 60) > 1 else '',
-            diff.seconds % 60,
-            's' if diff.seconds % 60 > 1 else ''
-        )
-    else:
-        duration = '{} hour{}, {} minute{}, {} second{}'.format(
-            floor(diff.seconds / 3600),
-            's' if floor(diff.seconds / 3600) > 1 else '',
-            floor((diff.seconds - 3600) / 60),
-            's' if floor((diff.seconds - 3600) / 60) > 1 else '',
-            diff.seconds % 60,
-            's' if diff.seconds % 60 > 1 else ''
-        )
+    h = floor(diff.seconds / 3600)
+    m = floor((diff.seconds - h * 3600) / 60)
+    s = diff.seconds % 60
+
+    duration = ''
+    if h > 0:
+        duration = '{} hour{}'.format(h, 's' if h > 1 else '')
+    if m > 0:
+        duration += '{}{} minute{}'.format(
+            '' if duration is '' else ', ', m, 's' if m > 1 else '')
+    if s > 0:
+        duration += '{}{} second{}'.format(
+            '' if duration is '' else ', ', s, 's' if s > 1 else '')
+
     return duration