Fix issue with ordering information when loading data from yaml source

Author: Thomas Rabaix

ioc/loader.py

@@ -1,9 +1,10 @@
 # vim: set fileencoding=utf-8 :
 
-import yaml
+import yaml, collections
 
 from ioc.component import Definition, Reference, WeakReference
 import ioc.helper, ioc.exceptions
+from misc import OrderedDictYAMLLoader
 
 class Loader(object):
     def fix_config(self, config):
@@ -20,7 +21,7 @@ def support(self, file):
     def load(self, file, container_builder):
 
         try:
-            data = yaml.load(open(file).read())
+            data = yaml.load(open(file).read(), OrderedDictYAMLLoader)
         except yaml.scanner.ScannerError, e:
             raise ioc.exceptions.LoadingError("file %s, \nerror: %s" % (file, e))
 

ioc/misc.py

@@ -0,0 +1,55 @@
+"""
+    The default yaml loader does not respect the ordering key while loading a dictionay.
+    This can lead to error while ordering is defining key by key
+
+    reference: https://gist.github.com/enaeseth/844388
+
+"""
+
+import yaml
+import yaml.constructor
+
+try:
+    # included in standard lib from Python 2.7
+    from collections import OrderedDict
+except ImportError:
+    # try importing the backported drop-in replacement
+    # it's available on PyPI
+    from ordereddict import OrderedDict
+
+class OrderedDictYAMLLoader(yaml.Loader):
+    """
+    A YAML loader that loads mappings into ordered dictionaries.
+    """
+
+    def __init__(self, *args, **kwargs):
+        yaml.Loader.__init__(self, *args, **kwargs)
+
+        self.add_constructor(u'tag:yaml.org,2002:map', type(self).construct_yaml_map)
+        self.add_constructor(u'tag:yaml.org,2002:omap', type(self).construct_yaml_map)
+
+    def construct_yaml_map(self, node):
+        data = OrderedDict()
+        yield data
+        value = self.construct_mapping(node)
+        data.update(value)
+
+    def construct_mapping(self, node, deep=False):
+        if isinstance(node, yaml.MappingNode):
+            self.flatten_mapping(node)
+        else:
+            raise yaml.constructor.ConstructorError(None, None,
+                'expected a mapping node, but found %s' % node.id, node.start_mark)
+
+        mapping = OrderedDict()
+        for key_node, value_node in node.value:
+            key = self.construct_object(key_node, deep=deep)
+            try:
+                hash(key)
+            except TypeError, exc:
+                raise yaml.constructor.ConstructorError('while constructing a mapping',
+                    node.start_mark, 'found unacceptable key (%s)' % exc, key_node.start_mark)
+            value = self.construct_object(value_node, deep=deep)
+            mapping[key] = value
+        return mapping
+