python/ovs/db/idl: getattr(Row) raises TypeError, not AttributeError.

In some cases getattr(Row instance, attrname) doesn't raise AttributeError,
but TypeError

> File "python/ovs/db/idl.py", line 554, in __getattr__
>     datum = self._data[column_name]
> TypeError: 'NoneType' object has no attribute '__getitem__'

So getattr(Row instance, attrname, default value) doesn't work.
This occurs when row._changes doesn't include attrname and row._data is None.
So teach Row.__getattr__ _data=None case.

Signed-off-by: Isaku Yamahata <[email protected]>
Signed-off-by: Ben Pfaff <[email protected]>

python/ovs/db/idl.py

@@ -548,6 +548,9 @@ def __getattr__(self, column_name):
 
         datum = self._changes.get(column_name)
         if datum is None:
+            if self._data is None:
+                raise AttributeError("%s instance has no attribute '%s'" %
+                                     (self.__class__.__name__, column_name))
             datum = self._data[column_name]
 
         return datum.to_python(_uuid_to_row)

tests/ovsdb-idl.at

@@ -439,3 +439,12 @@ OVSDB_CHECK_IDL_PY([external-linking idl, insert ops],
 002: i=2 k=1 ka=[1 2] l2= uuid=<1>
 003: done
 ]])
+
+OVSDB_CHECK_IDL_PY([getattr idl, insert ops],
+  [],
+  [['getattrtest']],
+  [[000: empty
+001: commit, status=success
+002: i=2 k=2 ka=[] l2= uuid=<0>
+003: done
+]])

tests/test-ovsdb.py

@@ -321,6 +321,14 @@ def idl_set(idl, commands, step):
             l1_1.i = 2
             l1_1.k = [l1_0]
             l1_1.ka = [l1_0, l1_1]
+        elif name == 'getattrtest':
+            l1 = txn.insert(idl.tables["link1"])
+            i = getattr(l1, 'i', 1)
+            assert i == 1
+            l1.i = 2
+            i = getattr(l1, 'i', 1)
+            assert i == 2
+            l1.k = [l1]
         else:
             sys.stderr.write("unknown command %s\n" % name)
             sys.exit(1)