initial commit

jsonpatch.py

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+# -*- coding: utf-8 -*-
+#
+# python-json-patch - An implementation of the JSON Patch format
+# https://github.com/stefankoegl/python-json-patch
+#
+# Copyright (c) 2011 Stefan Kögl <stefan@skoegl.net>
+# All rights reserved.
+#
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions
+# are met:
+#
+# 1. Redistributions of source code must retain the above copyright
+#    notice, this list of conditions and the following disclaimer.
+# 2. Redistributions in binary form must reproduce the above copyright
+#    notice, this list of conditions and the following disclaimer in the
+#    documentation and/or other materials provided with the distribution.
+# 3. The name of the author may not be used to endorse or promote products
+#    derived from this software without specific prior written permission.
+#
+# THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
+# IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+# OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
+# IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
+# INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+# NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+# DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+# THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
+# THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+#
+
+"""Apply JSON-Patches according to http://tools.ietf.org/html/draft-pbryan-json-patch-01"""
+
+# Will be parsed by setup.py to determine package metadata
+__author__ = 'Stefan Kögl <stefan@skoegl.net>'
+__version__ = '0.1'
+__website__ = 'https://github.com/stefankoegl/python-json-patch'
+__license__ = 'Modified BSD License'
+
+
+import copy
+import json
+
+
+class JsonPatchException(Exception):
+    pass
+
+
+class JsonPatch(object):
+    """ A JSON Patch is a list of Patch Operations """
+
+    def __init__(self, patch):
+        self.patch = patch
+
+        self.OPERATIONS = {
+            'remove': RemoveOperation,
+            'add': AddOperation,
+            'replace': ReplaceOperation,
+        }
+
+
+    @classmethod
+    def from_string(cls, patch_str):
+        patch = json.loads(patch_str)
+        return cls(patch)
+
+
+    def apply(self, obj):
+        """ Applies the patch to a copy of the given object """
+
+        obj = copy.deepcopy(obj)
+
+        for operation in self.patch:
+            op = self._get_operation(operation)
+            op.apply(obj)
+
+        return obj
+
+
+    def _get_operation(self, operation):
+        for action, op_cls in self.OPERATIONS.items():
+            if action in operation:
+                location = operation[action]
+                op = op_cls(location, operation)
+                return op
+
+        raise JsonPatchException("invalid operation '%s'" % operation)
+
+
+
+class PatchOperation(object):
+    """ A single operation inside a JSON Patch """
+
+    def __init__(self, location, operation):
+        self.location = location
+        self.operation = operation
+
+
+    def locate(self, obj, location, last_must_exist=True):
+        """ Walks through the object according to location
+
+        Returns the last step as (sub-object, last location-step) """
+
+        parts = location.split('/')
+        if parts.pop(0) != '':
+            raise JsonPatchException('location must starts with /')
+
+        for part in parts[:-1]:
+            obj, loc_part = self._step(obj, part)
+
+        _, last_loc = self._step(obj, parts[-1], must_exist=last_must_exist)
+        return obj, last_loc
+
+
+    def _step(self, obj, loc_part, must_exist=True):
+        """ Goes one step in a locate() call """
+
+        # Its not clear if a location "1" should be considered as 1 or "1"
+        # We prefer the integer-variant if possible
+        part_variants = self._try_parse(loc_part) + [loc_part]
+
+        for variant in part_variants:
+            try:
+                return obj[variant], variant
+            except:
+                continue
+
+        if must_exist:
+            raise JsonPatchException('key %s not found' % loc_part)
+        else:
+            return obj, part_variants[0]
+
+
+    @staticmethod
+    def _try_parse(val, cls=int):
+        try:
+            return [cls(val)]
+        except:
+            return []
+
+
+class RemoveOperation(PatchOperation):
+    """ Removes an object property or an array element
+
+    >>> obj = { 'baz': 'qux', 'foo': 'bar' }
+    >>> patch = JsonPatch( [ { 'remove': '/baz' } ] )
+    >>> patch.apply(obj)
+    {'foo': 'bar'}
+
+    >>> obj = { 'foo': [ 'bar', 'qux', 'baz' ] }
+    >>> patch = JsonPatch( [ { "remove": "/foo/1" } ] )
+    >>> patch.apply(obj)
+    {'foo': ['bar', 'baz']}
+    """
+
+    def apply(self, obj):
+        subobj, part = self.locate(obj, self.location)
+        del subobj[part]
+
+
+class AddOperation(PatchOperation):
+    """ Adds an object property or an array element
+
+    >>> obj = { "foo": "bar" }
+    >>> patch = JsonPatch([ { "add": "/baz", "value": "qux" } ])
+    >>> patch.apply(obj)
+    {'foo': 'bar', 'baz': 'qux'}
+
+    >>> obj = { "foo": [ "bar", "baz" ] }
+    >>> patch = JsonPatch([ { "add": "/foo/1", "value": "qux" } ])
+    >>> patch.apply(obj)
+    {'foo': ['bar', 'qux', 'baz']}
+    """
+
+    def apply(self, obj):
+        value = self.operation["value"]
+        subobj, part = self.locate(obj, self.location, last_must_exist=False)
+
+        if isinstance(subobj, list):
+            if part > len(subobj) or part < 0:
+                raise JsonPatchException("can't insert outside of list")
+
+            subobj.insert(part, value)
+
+        elif isinstance(subobj, dict):
+            if part in subobj:
+                raise JsonPatchException("object '%s' already exists" % part)
+
+            subobj[part] = value
+
+        else:
+            raise JsonPatchException("can't add to type '%s'" % subobj.__class__.__name__)
+
+
+class ReplaceOperation(PatchOperation):
+    """ Replaces a value
+
+    >>> obj = { "baz": "qux", "foo": "bar" }
+    >>> patch = JsonPatch([ { "replace": "/baz", "value": "boo" } ])
+    >>> patch.apply(obj)
+    {'foo': 'bar', 'baz': 'boo'}
+    """
+
+    def apply(self, obj):
+        location = self. operation["replace"]
+        value = self.operation["value"]
+        subobj, part = self.locate(obj, self.location)
+
+        if isinstance(subobj, list):
+            if part > len(subobj) or part < 0:
+                raise JsonPatchException("can't replace outside of list")
+
+        elif isinstance(subobj, dict):
+            if not part in subobj:
+                raise JsonPatchException("can't replace non-existant object '%s'" % part)
+
+        else:
+            raise JsonPatchException("can't replace in type '%s'" % subobj.__class__.__name__)
+
+        subobj[part] = value