If 'bool_from_string' provided a boolean just return it

Typically the pattern of the following happens:

>>> s = dict()
>>> v = s.get("blah", True)
>>> v = strutils.bool_from_string(v)

In this case we can avoid converting the value of 'v' to a bool
if it was already a boolean (and if it wasn't then the rest of
the code can be ran to attempt to convert it to one). This avoids
needlessly converting things from bool -> string -> bool which
is not really needed in this case.

Change-Id: Id7397e91e754ff2c63b3f112e95aedf82cd31717

oslo_utils/strutils.py

@@ -119,6 +119,8 @@ def bool_from_string(subject, strict=False, default=False):
     ValueError which is useful when parsing values passed in from an API call.
     Strings yielding False are 'f', 'false', 'off', 'n', 'no', or '0'.
     """
+    if isinstance(subject, bool):
+        return subject
     if not isinstance(subject, six.string_types):
         subject = six.text_type(subject)
 

oslo_utils/tests/test_strutils.py

@@ -30,6 +30,12 @@ load_tests = testscenarios.load_tests_apply_scenarios
 
 class StrUtilsTest(test_base.BaseTestCase):
 
+    @mock.patch("six.text_type")
+    def test_bool_bool_from_string_no_text(self, mock_text):
+        self.assertTrue(strutils.bool_from_string(True))
+        self.assertFalse(strutils.bool_from_string(False))
+        self.assertEqual(0, mock_text.call_count)
+
     def test_bool_bool_from_string(self):
         self.assertTrue(strutils.bool_from_string(True))
         self.assertFalse(strutils.bool_from_string(False))