Pointers¶
This module contains JSONPointer, the typed path abstraction used by built-in
and custom operations.
JSONPointer
¶
Bases: str, Generic[T_co, P_co]
A typed RFC 6901 JSON Pointer with Pydantic integration.
JSONPointer[T] (or JSONPointer[T, Backend]) is a string-like value (subclasses str)
that additionally:
- stores a parsed pointer backend (see
PointerBackend), - tracks a covariant type parameter
Tused to validate resolved targets, - provides convenience methods used by patch operations:
get,add,remove.
Important design semantics (intentional)¶
Typed pointers are enforced at runtime.
The type parameter T is not “just typing”; it is enforced whenever a value is read
through the pointer.
get(doc)always validates the resolved value againstT.add(doc, value)optionally validates the written value againstT(default: True).remove(doc)is intentionally type-gated: it first “reads” the target through the pointer, so removal can fail if the current value is not of typeT.
This makes patch semantics explicit:
- JSONPointer[JSONValue] is permissive (“remove anything JSON”).
- JSONPointer[JSONBoolean] is restrictive (“remove only if it is currently a boolean”).
- If you want to remove regardless of the current type, use a wider pointer type (e.g. JSONValue)
or define a dedicated permissive remove operation.
Pointer covariance is intentional.
JSONPointer is covariant in T. In practice this means you can often reuse a pointer instance
(including across composed operations) and preserve stricter guarantees.
Examples: if a custom op carries a JSONPointer[JSONBoolean], composing that op internally
using AddOp should keep the boolean-specific enforcement at runtime.
Backend semantics (advanced)¶
- Default backend:
jsonpointer.JsonPointer. - Custom backend: bound directly via
JSONPointer[T, Backend]. - Invalid pointer strings raise
InvalidJSONPointer. - Backend traversal failures in
get/add/removeare normalized intoPatchConflictError.
Mutation semantics:
- add and remove may mutate the document object they are given (or containers reachable
from it). The root pointer "" is the exception: setting the root returns a new document
value rather than mutating an existing container. Removing the root returns
MISSING to represent document deletion rather than a JSON null value.
A missing root document is handled as its own state: root get and root remove
fail, while root add recreates the document.
If you want to forbid root removal, it's easy to make a custom op!
- Whether these mutations affect the original caller-owned document is determined by the patch
engine (see _apply_ops(..., inplace=...)), which may deep-copy the input document.
JSONPointer values are intended to be created by Pydantic validation. Direct instantiation
is not permitted (except when running as __main__ for debugging).
Source code in jsonpatchx/pointer.py
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parent_ptr
property
¶
Return the backend pointer for this pointer's parent path.
parts
property
¶
A sequence of RFC6901-unescaped pointer components.
ptr
property
¶
The underlying pointer backend instance.
This is exposed for advanced users who provide a custom PointerBackend with additional APIs.
The patch engine relies only on the PointerBackend protocol.
type_param
property
¶
The expected type parameter T used to validate resolved targets.
add(doc, value)
¶
RFC 6902 add (type-gated).
Parameters:
| Name | Type | Description | Default |
|---|---|---|---|
doc
|
JSONValue
|
Target JSON document. |
required |
value
|
object
|
Value to add at this path, validated against |
required |
Returns:
| Type | Description |
|---|---|
JSONValue
|
The updated document. |
Raises:
| Type | Description |
|---|---|
PatchConflictError
|
If the target does not exist, if the target is not type |
Source code in jsonpatchx/pointer.py
get(doc)
¶
Resolve this pointer against doc and return the target value (type-gated).
Parameters:
| Name | Type | Description | Default |
|---|---|---|---|
doc
|
JSONValue
|
Target JSON document. |
required |
Returns:
| Type | Description |
|---|---|
T_co
|
The resolved value, validated against |
Raises:
| Type | Description |
|---|---|
PatchConflictError
|
If the target does not exist, or it is not type |
Source code in jsonpatchx/pointer.py
is_addable(doc, value=_Nothing)
¶
Return True if RFC 6902 add would succeed for this document.
Parameters:
| Name | Type | Description | Default |
|---|---|---|---|
doc
|
JSONValue
|
Target JSON document. |
required |
value
|
object
|
Optional value that would be written at this pointer. When
provided, it must conform to |
_Nothing
|
Returns:
| Type | Description |
|---|---|
bool
|
|
Source code in jsonpatchx/pointer.py
is_child_of(other)
¶
Check whether this pointer is a strict child of other.
other may be a JSONPointer or a pointer string; strings are parsed using this pointer's syntax.
Root is treated as a parent of all paths except itself.
Raises InvalidJSONPointer if comparison is called with an other pointer with different or invalid syntax.
Source code in jsonpatchx/pointer.py
is_gettable(doc)
¶
Return True if get(doc) would succeed.
Parameters:
| Name | Type | Description | Default |
|---|---|---|---|
doc
|
JSONValue
|
Target JSON document. |
required |
Returns:
| Type | Description |
|---|---|
bool
|
|
bool
|
|
Source code in jsonpatchx/pointer.py
is_parent_of(other)
¶
Check whether this pointer is a strict parent of other.
other may be a JSONPointer or a pointer string; strings are parsed using this pointer's syntax.
Root is treated as a parent of all paths except itself.
Raises InvalidJSONPointer if comparison is called with an other pointer with different or invalid syntax.
Source code in jsonpatchx/pointer.py
is_removable(doc)
¶
Return True if RFC 6902 remove would succeed for this document.
Parameters:
| Name | Type | Description | Default |
|---|---|---|---|
doc
|
JSONValue
|
Target JSON document. |
required |
Returns:
| Type | Description |
|---|---|
bool
|
|
Source code in jsonpatchx/pointer.py
is_root(doc)
¶
is_valid_type(target)
¶
Return True if target conforms to this pointer's type.
Parameters:
| Name | Type | Description | Default |
|---|---|---|---|
target
|
object
|
Candidate value to validate. |
required |
Returns:
| Type | Description |
|---|---|
bool
|
|
bool
|
otherwise |
Source code in jsonpatchx/pointer.py
parse(path, *, type_param=_Nothing, backend=None)
classmethod
¶
Parse a pointer string or instance using Pydantic validation.
Parameters:
| Name | Type | Description | Default |
|---|---|---|---|
path
|
str | Self | PointerBackend
|
Pointer string, parsed pointer, or pointer backend instance. |
required |
type_param
|
TypeForm[Any] | object
|
Type enforced when the pointer is exercised. |
_Nothing
|
backend
|
type[PointerBackend] | None
|
Optional concrete backend class. When omitted, the built-in RFC 6901 backend is used. |
None
|
Returns:
| Type | Description |
|---|---|
JSONPointer[Any, PointerBackend]
|
A validated |
Raises:
| Type | Description |
|---|---|
InvalidJSONPointer
|
If the pointer string, backend, or generic parameters are invalid. |
Notes
type_param technically places the covariant T parameter in an
input position, which would normally be an unsound public API
shape. That tradeoff is intentional here because parse() is only
a convenience constructor around Pydantic validation. Normal
construction happens through Pydantic on an already-specialized
JSONPointer[...] type, so callers are not meant to treat
parse() as the primary semantic surface for consuming T.
Source code in jsonpatchx/pointer.py
remove(doc)
¶
RFC 6902 remove (type-gated). Removal of the root returns MISSING.
Parameters:
| Name | Type | Description | Default |
|---|---|---|---|
doc
|
JSONValue
|
Target JSON document. |
required |
Returns:
| Type | Description |
|---|---|
JSONValue
|
The updated document. |
Raises:
| Type | Description |
|---|---|
PatchConflictError
|
If the target does not exist, or it is not type |