Revising method for parsing ranges from --limit subsets

Also added a new test (test_subset_range) for future validation.

Fixes #4620

lib/ansible/inventory/__init__.py

@@ -207,24 +207,19 @@ class Inventory(object):
         a tuple of (start, stop) or None
         """
 
-        if not "[" in pattern or pattern.startswith('~'):
-            return (pattern, None)
-        (first, rest) = pattern.split("[")
-        rest = rest.replace("]","")
-        try:
-            # support selectors like webservers[0]
-            x = int(rest)
-            return (first, (x,x)) 
-        except:
-            pass
-        if "-" in rest:
-            (left, right) = rest.split("-",1)
-            return (first, (left, right))
-        elif ":" in rest:
-            (left, right) = rest.split(":",1)
-            return (first, (left, right))
+        # The regex used to match on the range, which can be [x] or [x-y].
+        pattern_re = re.compile("^(.*)\[([0-9]+)(?:(?:-)([0-9]+))?\](.*)$")
+        m = pattern_re.match(pattern)
+        if m:
+            (target, first, last, rest) = m.groups()
+            first = int(first)
+            if last:
+                last = int(last)
             else:
-            return (first, (rest, rest))
+                last = first
+            return (target, (first, last))
+        else:
+            return (pattern, None)
 
     def _apply_ranges(self, pat, hosts):
         """

test/TestInventory.py

@@ -206,6 +206,11 @@ class TestInventory(unittest.TestCase):
         inventory.subset('odin;thor,loki')
         self.assertEqual(sorted(inventory.list_hosts()),  sorted(['thor','odin','loki']))
 
+    def test_subset_range(self):
+        inventory = self.simple_inventory()
+        inventory.subset('greek[0-2];norse[0]')
+        self.assertEqual(sorted(inventory.list_hosts()),  sorted(['zeus','hera','thor']))
+
     def test_subset_filename(self):
         inventory = self.simple_inventory()
         inventory.subset('@' + os.path.join(self.test_dir, 'restrict_pattern'))