Support for direct deep dictionary value retrieval

examples/deep/main.fmf

@@ -8,3 +8,14 @@
 
 /one/two/three:
     key: value
+
+
+# Values from a deep dictionary can be retrieved easily using the
+# get() method which supports providing default values as well.
+# Example: tree.get(['hardware', 'memory', 'size'], default)
+
+hardware:
+    memory:
+        size: 8
+    network:
+        model: e1000

fmf/base.py

@@ -174,11 +174,34 @@ def update(self, data):
         log.debug("Data for '{0}' updated.".format(self))
         log.data(pretty(self.data))
 
-    def get(self, name=None):
-        """ Get desired attribute """
+    def get(self, name=None, default=None):
+        """
+        Get attribute value or return default
+
+        Whole data dictionary is returned when no attribute provided.
+        Supports direct values retrieval from deep dictionaries as well.
+        Dictionary path should be provided as list. The following two
+        examples are equal:
+
+        tree.data['hardware']['memory']['size']
+        tree.get(['hardware', 'memory', 'size'])
+
+        However the latter approach will also correctly handle providing
+        default value when any of the dictionary keys does not exist.
+
+        """
+        # Return the whole dictionary if no attribute specified
         if name is None:
             return self.data
-        return self.data[name]
+        if not isinstance(name, list):
+            name = [name]
+        data = self.data
+        try:
+            for key in name:
+                data = data[key]
+        except KeyError:
+            return default
+        return data
 
     def child(self, name, data, source=None):
         """ Create or update child with given data """

tests/test_base.py

@@ -73,6 +73,14 @@ def test_deep_hierarchy(self):
         deep = Tree(EXAMPLES + "deep")
         assert len(deep.children) == 1
 
+    def test_deep_dictionary(self):
+        """ Get value from a deep dictionary """
+        deep = Tree(EXAMPLES + "deep")
+        assert deep.data['hardware']['memory']['size'] == 8
+        assert deep.get(['hardware', 'memory', 'size']) == 8
+        assert deep.get(['hardware', 'bad', 'size'], 12) == 12
+        assert deep.get('nonexistent', default=3) == 3
+
     def test_merge(self):
         """ Attribute merging """
         child = self.merge.find('/parent/child')
@@ -123,3 +131,4 @@ def test_yaml_syntax_errors(self):
         with pytest.raises(utils.FileError):
             tree = fmf.Tree(path)
         rmtree(path)
+