Add tests and fixes for update

1 files changed, 33 insertions, 5 deletions

diff --git a/jsonpath_rw/jsonpath.py b/jsonpath_rw/jsonpath.py
index 395516e..93d7b81 100644
--- a/jsonpath_rw/jsonpath.py
+++ b/jsonpath_rw/jsonpath.py
@@ -26,7 +26,11 @@ class JSONPath(object):
         raise NotImplementedError()
 
     def update(self, data, val):
-        "Returns `data` with the specified path replaced by `val`"
+        """
+        Returns `data` with the specified path replaced by `val`. Only updates
+        if the specified path exists.
+        """
+
         raise NotImplementedError()
 
     def child(self, child):
@@ -340,8 +344,30 @@ class Descendants(JSONPath):
         return False
 
     def update(self, data, val):
-        for datum in self.left.find(data):
-            self.right.update(datum.value, val)
+        # Get all left matches into a list
+        left_matches = self.left.find(data)
+        if not isinstance(left_matches, list):
+            left_matches = [left_matches]
+
+        def update_recursively(data):
+            # Update only mutable values corresponding to JSON types
+            if not (isinstance(data, list) or isinstance(data, dict)):
+                return
+
+            self.right.update(data, val)
+
+            # Manually do the * or [*] to avoid coercion and recurse just the right-hand pattern
+            if isinstance(data, list):
+                for i in range(0, len(data)):
+                    update_recursively(data[i])
+
+            elif isinstance(data, dict):
+                for field in data.keys():
+                    update_recursively(data[field])
+
+        for submatch in left_matches:
+            update_recursively(submatch.value)
+
         return data
 
     def __str__(self):
@@ -432,7 +458,8 @@ class Fields(JSONPath):
 
     def update(self, data, val):
         for field in self.reified_fields(DatumInContext.wrap(data)):
-            data[field] = val
+            if field in data:
+                data[field] = val
         return data
 
     def __str__(self):
@@ -466,7 +493,8 @@ class Index(JSONPath):
             return []
 
     def update(self, data, val):
-        data[self.index] = val
+        if len(data) > self.index:
+            data[self.index] = val
         return data
 
     def __eq__(self, other):