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Merged
stefankoegl merged 2 commits into from
Nov 2, 2026
Merged

Attach failing operation to JsonPatchException as op #247

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5eccc03
Attach failing operation to JsonPatchException as `op`
Nov 2, 2026
bafa36c
Report move/copy and string-entry failures against the original opera…
claude Nov 2, 2026
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107 changes: 67 additions & 40 deletions jsonpatch.py
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Original file line number Diff line number Diff line change
Expand Up @@ -63,6 +63,19 @@
class JsonPatchException(Exception):
"""Base Json Patch exception"""

def __init__(self, *args, **kwargs):
"""Initialize a new instance of a JsonPatchException

:param op: The operation that failed. It is attached to the exception
so that callers can inspect (or modify) the failing patch
operation. This is either a :class:`PatchOperation`
instance or, if the operation could not be constructed,
the raw operation object.
:type op: PatchOperation or dict or None
"""
self.op = kwargs.pop('op', None)
super(JsonPatchException, self).__init__(*args, **kwargs)


class InvalidJsonPatch(JsonPatchException):
""" Raised if an invalid JSON Patch is created """
Expand Down Expand Up @@ -173,7 +186,7 @@ def __init__(self, operation, pointer_cls=JsonPointer):
self.pointer_cls = pointer_cls

if not operation.__contains__('path'):
raise InvalidJsonPatch("Operation must have a 'path' member")
raise InvalidJsonPatch("Operation must have a 'path' member", op=operation)

if isinstance(operation['path'], self.pointer_cls):
self.location = operation['path'].path
Expand All @@ -183,7 +196,7 @@ def __init__(self, operation, pointer_cls=JsonPointer):
try:
self.pointer = self.pointer_cls(self.location)
except TypeError:
raise InvalidJsonPatch("Invalid 'path'")
raise InvalidJsonPatch("Invalid 'path'", op=operation)

self.operation = operation

Expand All @@ -194,15 +207,15 @@ def _from_pointer(self):
from_ptr = self.operation['from']
except KeyError:
raise InvalidJsonPatch(
"The operation does not contain a 'from' member")
"The operation does not contain a 'from' member", op=self)

if isinstance(from_ptr, self.pointer_cls):
return from_ptr

try:
return self.pointer_cls(from_ptr)
except TypeError:
raise InvalidJsonPatch("Invalid 'from'")
raise InvalidJsonPatch("Invalid 'from'", op=self)

def apply(self, obj):
"""Abstract method that applies a patch operation to the specified object."""
Expand Down Expand Up @@ -253,7 +266,7 @@ def apply(self, obj):
subobj, part = self.pointer.to_last(obj)

if part is None:
raise JsonPatchConflict("can't remove the whole document")
raise JsonPatchConflict("can't remove the whole document", op=self)

if isinstance(subobj, Sequence) and not isinstance(part, int):
raise JsonPointerException("invalid array index '{0}'".format(part))
Expand All @@ -262,9 +275,9 @@ def apply(self, obj):
del subobj[part]
except (KeyError, IndexError):
msg = "can't remove a non-existent object '{0}'".format(part)
raise JsonPatchConflict(msg)
raise JsonPatchConflict(msg, op=self)
except TypeError as ex:
raise JsonPatchConflict(str(ex))
raise JsonPatchConflict(str(ex), op=self)

return obj

Expand All @@ -277,7 +290,7 @@ def apply(self, obj):
value = self.operation["value"]
except KeyError:
raise InvalidJsonPatch(
"The operation does not contain a 'value' member")
"The operation does not contain a 'value' member", op=self)

# Insert a copy so the document does not share mutable values with
# the patch; otherwise later operations would modify the patch itself.
Expand All @@ -294,7 +307,7 @@ def _add(self, obj, value):
subobj.append(value) # pylint: disable=E1103

elif part > len(subobj) or part < 0:
raise JsonPatchConflict("can't insert outside of list")
raise JsonPatchConflict("can't insert outside of list", op=self)
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else:
subobj.insert(part, value) # pylint: disable=E1103
Expand All @@ -303,7 +316,7 @@ def _add(self, obj, value):
subobj[part] = value

else:
raise JsonPatchConflict("unable to fully resolve json pointer {0}, part {1}".format(self.location, part))
raise JsonPatchConflict("unable to fully resolve json pointer {0}, part {1}".format(self.location, part), op=self)
return obj


Expand All @@ -315,7 +328,7 @@ def apply(self, obj):
value = self.operation["value"]
except KeyError:
raise InvalidJsonPatch(
"The operation does not contain a 'value' member")
"The operation does not contain a 'value' member", op=self)

# copied for the same reason as in AddOperation.apply
value = copy.deepcopy(value)
Expand All @@ -329,17 +342,17 @@ def apply(self, obj):
# '-' only refers to the (nonexistent) element after the end of
# an array; for an object it is an ordinary member name
if part == "-":
raise InvalidJsonPatch("'path' with '-' can't be applied to 'replace' operation")
raise InvalidJsonPatch("'path' with '-' can't be applied to 'replace' operation", op=self)

if part >= len(subobj) or part < 0:
raise JsonPatchConflict("can't replace outside of list")
raise JsonPatchConflict("can't replace outside of list", op=self)

elif isinstance(subobj, MutableMapping):
if part not in subobj:
msg = "can't replace a non-existent object '{0}'".format(part)
raise JsonPatchConflict(msg)
raise JsonPatchConflict(msg, op=self)
else:
raise JsonPatchConflict("unable to fully resolve json pointer {0}, part {1}".format(self.location, part))
raise JsonPatchConflict("unable to fully resolve json pointer {0}, part {1}".format(self.location, part), op=self)

subobj[part] = value
return obj
Expand All @@ -355,7 +368,7 @@ def apply(self, obj):
# shifts its siblings, so the target would resolve to a different
# location. This also covers moving the whole document ('from' is "").
if self.pointer != from_ptr and self.pointer.contains(from_ptr):
raise JsonPatchConflict('Cannot move values into their own children')
raise JsonPatchConflict('Cannot move values into their own children', op=self)

subobj, part = _to_existing_last(from_ptr, obj)

Expand All @@ -366,22 +379,29 @@ def apply(self, obj):
try:
value = subobj[part]
except (KeyError, IndexError) as ex:
raise JsonPatchConflict(str(ex))
raise JsonPatchConflict(str(ex), op=self)

# If source and target are equal, this is a no-op
if self.pointer == from_ptr:
return obj

obj = RemoveOperation({
'op': 'remove',
'path': self.operation['from']
}, pointer_cls=self.pointer_cls).apply(obj)

# the value has been detached from its old location, so no copy needed
obj = AddOperation({
'op': 'add',
'path': self.location,
}, pointer_cls=self.pointer_cls)._add(obj, value)
try:
obj = RemoveOperation({
'op': 'remove',
'path': self.operation['from']
}, pointer_cls=self.pointer_cls).apply(obj)

# the value has been detached from its old location, so no copy
# needed
obj = AddOperation({
'op': 'add',
'path': self.location,
}, pointer_cls=self.pointer_cls)._add(obj, value)
except JsonPatchException as ex:
# report the failure against this operation rather than the
# internal, synthetic remove / add operations
ex.op = self
raise

return obj

Expand Down Expand Up @@ -422,18 +442,18 @@ def apply(self, obj):
else:
val = self.pointer.walk(subobj, part)
except JsonPointerException as ex:
raise JsonPatchTestFailed(str(ex))
raise JsonPatchTestFailed(str(ex), op=self)

try:
value = self.operation['value']
except KeyError:
raise InvalidJsonPatch(
"The operation does not contain a 'value' member")
"The operation does not contain a 'value' member", op=self)

if not _json_equal(val, value):
msg = '{0} ({1}) is not equal to tested value {2} ({3})'
raise JsonPatchTestFailed(msg.format(val, type(val),
value, type(value)))
value, type(value)), op=self)

return obj

Expand All @@ -448,13 +468,19 @@ def apply(self, obj):
try:
value = copy.deepcopy(subobj if part is None else subobj[part])
except (KeyError, IndexError) as ex:
raise JsonPatchConflict(str(ex))
raise JsonPatchConflict(str(ex), op=self)

# value is already a deep copy, no need to copy it again
obj = AddOperation({
'op': 'add',
'path': self.location,
}, pointer_cls=self.pointer_cls)._add(obj, value)
try:
obj = AddOperation({
'op': 'add',
'path': self.location,
}, pointer_cls=self.pointer_cls)._add(obj, value)
except JsonPatchException as ex:
# report the failure against this operation rather than the
# internal, synthetic add operation
ex.op = self
raise

return obj

Expand Down Expand Up @@ -547,7 +573,8 @@ def __init__(self, patch, pointer_cls=JsonPointer):
# of mappings, this won't raise.
if isinstance(op, (str, bytes)):
raise InvalidJsonPatch("Document is expected to be sequence of "
"operations, got a sequence of strings.")
"operations, got a sequence of strings.",
op=op)

self._get_operation(op)

Expand Down Expand Up @@ -671,18 +698,18 @@ def apply(self, obj, in_place=False):

def _get_operation(self, operation):
if not isinstance(operation, Mapping):
raise InvalidJsonPatch("Operation must be an object")
raise InvalidJsonPatch("Operation must be an object", op=operation)
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if 'op' not in operation:
raise InvalidJsonPatch("Operation does not contain 'op' member")
raise InvalidJsonPatch("Operation does not contain 'op' member", op=operation)

op = operation['op']

if not isinstance(op, (str, bytes)):
raise InvalidJsonPatch("Operation's op must be a string")
raise InvalidJsonPatch("Operation's op must be a string", op=operation)

if op not in self.operations:
raise InvalidJsonPatch("Unknown operation {0!r}".format(op))
raise InvalidJsonPatch("Unknown operation {0!r}".format(op), op=operation)

cls = self.operations[op]
return cls(operation, pointer_cls=self.pointer_cls)
Expand Down
62 changes: 62 additions & 0 deletions tests.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1961,6 +1961,67 @@ def test_json_patch_with_prefix_pointer(self):
self.assertEqual(res, {'foo': {'bar': {'baz': 'qux'}}})


class ExceptionOperationTests(unittest.TestCase):
""" The failing operation is attached to raised exceptions """

def test_conflict_has_operation(self):
patch = jsonpatch.JsonPatch([{'op': 'remove', 'path': '/missing'}])
with self.assertRaises(jsonpatch.JsonPatchConflict) as cm:
patch.apply({'foo': 1})
self.assertIsInstance(cm.exception.op, jsonpatch.RemoveOperation)
self.assertEqual(cm.exception.op.location, '/missing')
self.assertEqual(str(cm.exception),
"can't remove a non-existent object 'missing'")

def test_test_failed_has_operation(self):
patch = jsonpatch.JsonPatch([{'op': 'test', 'path': '/foo', 'value': 2}])
with self.assertRaises(jsonpatch.JsonPatchTestFailed) as cm:
patch.apply({'foo': 1})
self.assertIsInstance(cm.exception.op, jsonpatch.TestOperation)

def test_invalid_patch_has_raw_operation(self):
operation = {'op': 'frobnicate', 'path': '/foo'}
with self.assertRaises(jsonpatch.InvalidJsonPatch) as cm:
jsonpatch.apply_patch({}, [operation])
self.assertIs(cm.exception.op, operation)

def test_move_failed_add_reports_move_operation(self):
patch = jsonpatch.JsonPatch(
[{'op': 'move', 'from': '/foo', 'path': '/bar/5'}])
with self.assertRaises(jsonpatch.JsonPatchConflict) as cm:
patch.apply({'foo': 1, 'bar': []})
self.assertIsInstance(cm.exception.op, jsonpatch.MoveOperation)
self.assertIs(cm.exception.op.operation, patch.patch[0])

def test_move_failed_remove_reports_move_operation(self):
# the value can be read from the immutable tuple, but the internal
# remove operation fails
patch = jsonpatch.JsonPatch(
[{'op': 'move', 'from': '/foo/0', 'path': '/bar'}])
with self.assertRaises(jsonpatch.JsonPatchConflict) as cm:
patch.apply({'foo': (1, 2)})
self.assertIsInstance(cm.exception.op, jsonpatch.MoveOperation)
self.assertIs(cm.exception.op.operation, patch.patch[0])

def test_copy_failed_add_reports_copy_operation(self):
patch = jsonpatch.JsonPatch(
[{'op': 'copy', 'from': '/foo', 'path': '/bar/5'}])
with self.assertRaises(jsonpatch.JsonPatchConflict) as cm:
patch.apply({'foo': 1, 'bar': []})
self.assertIsInstance(cm.exception.op, jsonpatch.CopyOperation)
self.assertIs(cm.exception.op.operation, patch.patch[0])

def test_string_entry_has_raw_operation(self):
with self.assertRaises(jsonpatch.InvalidJsonPatch) as cm:
jsonpatch.JsonPatch(['invalid operation'])
self.assertEqual(cm.exception.op, 'invalid operation')

def test_op_defaults_to_none(self):
ex = jsonpatch.JsonPatchException('message')
self.assertIsNone(ex.op)
self.assertEqual(str(ex), 'message')


class CustomOperationTests(unittest.TestCase):

def test_custom_operation(self):
Expand Down Expand Up @@ -2427,6 +2488,7 @@ def get_suite():
suite.addTest(unittest.defaultTestLoader.loadTestsFromTestCase(OperationLocationTests))
suite.addTest(unittest.defaultTestLoader.loadTestsFromTestCase(CustomJsonPointerTests))
suite.addTest(unittest.defaultTestLoader.loadTestsFromTestCase(CustomOperationTests))
suite.addTest(unittest.defaultTestLoader.loadTestsFromTestCase(ExceptionOperationTests))
suite.addTest(unittest.defaultTestLoader.loadTestsFromTestCase(CommandLineTests))
suite.addTest(unittest.defaultTestLoader.loadTestsFromTestCase(DocumentationTests))
return suite
Expand Down
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