Raise a specific exception instead of generic AttributeError

Currently we raise an AttributeError when expected attribute is missing
from the response. This is not very developer-friendly, so this patch
creates a new exception (derived from AttributeError for compatibility)
for this purpose.

Change-Id: If2ac03dcd410d451dc7bbfe7bbd0b145da201c9a
Related-Bug: #1550328

dracclient/exceptions.py

@@ -39,6 +39,10 @@ class DRACEmptyResponseField(BaseClientException):
     msg_fmt = ("Attribute '%(attr)s' is not nullable, but no value received")
 
 
+class DRACMissingResponseField(BaseClientException, AttributeError):
+    msg_fmt = ("Attribute '%(attr)s' is missing from the response")
+
+
 class InvalidParameterValue(BaseClientException):
     msg_fmt = '%(reason)s'
 

dracclient/tests/test_utils.py

@@ -40,7 +40,8 @@ class UtilsTestCase(base.BaseTest):
         self.assertEqual('1', val)
 
     def test_get_wsman_resource_attr_missing_attr(self):
-        expected_message = ("Could not find attribute 'HyperThreadingEnabled'")
+        expected_message = ("Attribute 'HyperThreadingEnabled' is missing "
+                            "from the response")
         doc = etree.fromstring(
             test_utils.InventoryEnumerations[
                 uris.DCIM_CPUView]['missing_flags'])
@@ -48,7 +49,7 @@ class UtilsTestCase(base.BaseTest):
                               find_all=True)
 
         self.assertRaisesRegexp(
-            AttributeError, re.escape(expected_message),
+            exceptions.DRACMissingResponseField, re.escape(expected_message),
             utils.get_wsman_resource_attr, cpus[0], uris.DCIM_CPUView,
             'HyperThreadingEnabled', allow_missing=False)
 

dracclient/utils.py

@@ -58,9 +58,9 @@ def get_wsman_resource_attr(doc, resource_uri, attr_name, nullable=False,
                      value of True. In this case, it will return None.
     :param allow_missing: if set to True, attributes missing from the XML
                           document will return None instead of raising
-                          AttributeError.
-    :raises: AttributeError if the attribute is missing from the XML doc and
-             allow_missing is False.
+                          DRACMissingResponseField.
+    :raises: DRACMissingResponseField if the attribute is missing from the XML
+             doc and allow_missing is False.
     :raises: DRACEmptyResponseField if the attribute is present in the XML doc
              but it has no text and nullable is False.
     :returns: value of the attribute
@@ -71,7 +71,7 @@ def get_wsman_resource_attr(doc, resource_uri, attr_name, nullable=False,
         if allow_missing:
             return
         else:
-            raise AttributeError("Could not find attribute '%s'" % (attr_name))
+            raise exceptions.DRACMissingResponseField(attr=attr_name)
 
     if not nullable:
         if item.text is None: