1 files changed, 76 insertions, 0 deletions
diff --git a/jsonschema/exceptions.py b/jsonschema/exceptions.py
index 26fafbe..6b863ec 100644
--- a/jsonschema/exceptions.py
+++ b/jsonschema/exceptions.py
@@ -136,6 +136,82 @@ class FormatError(Exception):
         __str__ = __unicode__
 
 
+class ErrorTree(object):
+    """
+    ErrorTrees make it easier to check which validations failed.
+
+    """
+
+    _instance = _unset
+
+    def __init__(self, errors=()):
+        self.errors = {}
+        self._contents = collections.defaultdict(self.__class__)
+
+        for error in errors:
+            container = self
+            for element in error.path:
+                container = container[element]
+            container.errors[error.validator] = error
+
+            self._instance = error.instance
+
+    def __contains__(self, index):
+        """
+        Check whether ``instance[index]`` has any errors.
+
+        """
+
+        return index in self._contents
+
+    def __getitem__(self, index):
+        """
+        Retrieve the child tree one level down at the given ``index``.
+
+        If the index is not in the instance that this tree corresponds to and
+        is not known by this tree, whatever error would be raised by
+        ``instance.__getitem__`` will be propagated (usually this is some
+        subclass of :class:`LookupError`.
+
+        """
+
+        if self._instance is not _unset and index not in self:
+            self._instance[index]
+        return self._contents[index]
+
+    def __setitem__(self, index, value):
+        self._contents[index] = value
+
+    def __iter__(self):
+        """
+        Iterate (non-recursively) over the indices in the instance with errors.
+
+        """
+
+        return iter(self._contents)
+
+    def __len__(self):
+        """
+        Same as :attr:`total_errors`.
+
+        """
+
+        return self.total_errors
+
+    def __repr__(self):
+        return "<%s (%s total errors)>" % (self.__class__.__name__, len(self))
+
+    @property
+    def total_errors(self):
+        """
+        The total number of errors in the entire tree, including children.
+
+        """
+
+        child_errors = sum(len(tree) for _, tree in iteritems(self._contents))
+        return len(self.errors) + child_errors
+
+
 def by_relevance(weak=WEAK_MATCHES, strong=STRONG_MATCHES):
     def relevance(error):
         validator = error.validator