Fix/h5store setdefault (#180)

* Extend unit test to check H5Store.setdefault() return value.

* Add explicit setdefault() functions to H5Store and H5Group.

This ensures that for example, the return value of
`h5store.setdefault('foo', dict())` is an instance of `H5Group` and
not just a dictionary.

* Update changelog.

changelog.txt

@@ -21,6 +21,7 @@ next
 
  - Add command line options ``--sp`` and ``--doc`` for ``signac find`` that allow users to display key-value pairs of the state point and document in combination with the job id (#97, #146).
  - Fix: Searches for whole numbers will match all numerically matching integers regardless of whether they are stored as decimals or whole numbers (#169).
+ - Fix: Passing an instance of dict to `H5Store.setdefault()` will return an instance of `H5Group` instead of a dict (#180).
 
 
 [1.0.0] -- 2019-02-28

signac/core/h5store.py

@@ -210,6 +210,10 @@ def __setattr__(self, key, value):
         else:
             self.__setitem__(key, value)
 
+    def setdefault(self, key, value):
+        super(H5Group, self).setdefault(key, value)
+        return self.__getitem__(key)
+
     def __iter__(self):
         # The generator below should be refactored to use 'yield from'
         # once we drop Python 2.7 support.
@@ -433,6 +437,10 @@ def __delattr__(self, key):
         else:
             self.__delitem__(key)
 
+    def setdefault(self, key, value):
+        super(H5Store, self).setdefault(key, value)
+        return self.__getitem__(key)
+
     def __iter__(self):
         with _ensure_open(self):
             # The generator below should be refactored to use 'yield from'

tests/test_h5store.py

@@ -177,7 +177,11 @@ def test_set_get_explicit_nested(self):
         with self.open_h5store() as h5s:
             key = 'setgetexplicitnested'
             d = self.get_testdata()
-            h5s.setdefault('a', dict())
+            self.assertNotIn('a', h5s)
+            ret = h5s.setdefault('a', dict())
+            self.assertIn('a', h5s)
+            self.assertEqual(ret, h5s['a'])
+            self.assertTrue(hasattr(ret, '_store'))  # is an H5Group object
             child1 = h5s['a']
             child2 = h5s['a']
             self.assertEqual(child1, child2)