Change Metadata keys/items/values to match dict interface

Return KeysView, ItemsView, and ValuesView types.

python/lsst/verify/jobmetadata.py

@@ -167,30 +167,41 @@ def _repr_html_(self):
         return self.__str__()
 
     def keys(self):
-        """Get a `list` of metadata keys.
+        """Get the metadata keys.
 
         Returns
         -------
-        keys : `list` of `str`
-            These keys keys can be used to access metadata values (like a
-            `dict`).
+        keys : `~collections.abc.KeysView` [`str`]
+            The keys that can be used to access metadata values (like a
+            `dict`). Set-like.
         """
-        return [key for key in self]
+        self._refresh_chainmap()
+        return self._chain.keys()
 
     def items(self):
         """Iterate over key-value metadata pairs.
 
         Yields
         ------
-        item : `tuple`
-            A metadata item is a tuple of:
+        item : `~collections.abc.ItemsView`
+            An iterable over metadata items that are a tuple of:
 
             - Key (`str`).
             - Value (object).
         """
         self._refresh_chainmap()
-        for item in self._chain.items():
-            yield item
+        return self._chain.items()
+
+    def values(self):
+        """Iterate over metadata values.
+
+        Returns
+        ------
+        items : `~collections.abc.ValuesView`
+            An iterable over all the values.
+        """
+        self._refresh_chainmap()
+        return self._chain.values()
 
     def update(self, data):
         """Update metadata with key-value pairs from a `dict`-like object.

tests/test_job.py

@@ -108,18 +108,20 @@ def test_job(self):
         self.assertNotIn('dataset', job.meta)
 
         self.assertEqual(
-            set(job.meta.keys()),
+            job.meta.keys(),
             set(['job-level-key', 'test.PhotRms.note'])
         )
         self.assertEqual(
             set([key for key in job.meta]),
             set(['job-level-key', 'test.PhotRms.note'])
         )
         keys = set()
-        for key, value in job.meta.items():
+        for key, _ in job.meta.items():
             keys.add(key)
         self.assertEqual(keys, set(['job-level-key', 'test.PhotRms.note']))
 
+        self.assertEqual(len(job.meta.keys()), len(job.meta.values()))
+
         # Add a new measurement
         m = Measurement('test.PhotMedian', 28.5 * u.mag,
                         notes={'aperture_corr': True})