add JsonPointer.to_last() for use in jsonpatch

1 files changed, 30 insertions, 5 deletions

diff --git a/jsonpointer.py b/jsonpointer.py
index 3a86773..fe3cecf 100644
--- a/jsonpointer.py
+++ b/jsonpointer.py
@@ -146,6 +146,14 @@ class JsonPointer(object):
         self.parts = parts
 
 
+    def to_last(self, doc, default=_nothing):
+        """ Resolves ptr until the last step, returns (sub-doc, last-step) """
+
+        for part in self.parts[:-1]:
+            doc = self.walk(doc, part)
+
+        return doc, self.get_part(doc, self.parts[-1])
+
 
     def resolve(self, doc, default=_nothing):
         """Resolves the pointer against doc and returns the referenced object"""
@@ -208,9 +216,31 @@ class JsonPointer(object):
         return doc[part]
 
 
+    def get_part(self, doc, part):
+        """ Returns the next step in the correct type """
+
+        if isinstance(doc, dict):
+            return part
+
+        elif isinstance(doc, list):
+
+            if part == '-':
+                return part
+
+            try:
+                return int(part)
+            except ValueError:
+                raise JsonPointerException("'%s' is not a valid list index" % (part, ))
+
+        else:
+            raise JsonPointerException("Unknown document type '%s'" % (doc.__class__,))
+
+
     def walk(self, doc, part):
         """ Walks one step in doc and returns the referenced part """
 
+        part = self.get_part(doc, part)
+
         if isinstance(doc, dict):
             try:
                 return doc[part]
@@ -224,11 +254,6 @@ class JsonPointer(object):
                 return EndOfList(doc)
 
             try:
-                part = int(part)
-            except ValueError:
-                raise JsonPointerException("'%s' is not a valid list index" % (part, ))
-
-            try:
                 return doc[part]
 
             except IndexError: