feat: JSONPointer.exists(), closes #19

CHANGELOG.md

@@ -11,6 +11,7 @@
 - Added a command line interface, exposing JSONPath, JSON Pointer and JSON Patch features.
 - Added `JSONPointer.parent()`, a method that returns a the parent of the pointer, as a new `JSONPointer`.
 - Implemented `JSONPointer.__truediv__()` to allow creation of child pointers from an existing pointer.
+- Added `JSONPointer.exists()`, a method that returns `True` if a the pointer can be resolved against some data, or `False` otherwise.
 
 ## Version 0.8.1
 

jsonpath/pointer.py

@@ -278,6 +278,9 @@ def from_parts(
  before parsing the pointer.
  uri_decode: If `True`, the pointer will be unescaped using _urllib_
  before being parsed.
+
+ Returns:
+ A new `JSONPointer` built from _parts_.
  """
  _parts = (str(p) for p in parts)
  if uri_decode:
@@ -317,6 +320,29 @@ def __eq__(self, other: object) -> bool:
  def __repr__(self) -> str:
  return f"JSONPointer({self._s!r})"
 
+ def exists(
+ self, data: Union[str, IOBase, Sequence[object], Mapping[str, object]]
+ ) -> bool:
+ """Return _True_ if this pointer can be resolved against _data_.
+
+ Note that `JSONPointer.resolve()` can return legitimate falsy values
+ that form part of the target JSON document. This method will return
+ `True` if a falsy value is found.
+
+ Args:
+ data: The target JSON "document" or equivalent Python objects.
+
+ Returns:
+ _True_ if this pointer can be resolved against _data_, or _False_
+ otherwise.
+
+ """
+ try:
+ self.resolve(data)
+ except JSONPointerResolutionError:
+ return False
+ return True
+
  def parent(self) -> JSONPointer:
  """Return this pointer's parent, as a new `JSONPointer`.
 

tests/test_json_pointer.py

@@ -256,3 +256,10 @@ def test_join_pointers() -> None:
 
  with pytest.raises(TypeError):
  pointer / 0
+
+
+def test_pointer_exists() -> None:
+ data = {"some": {"thing": [1, 2, 3]}, "other": None}
+ assert JSONPointer("/some/thing").exists(data) is True
+ assert JSONPointer("/other").exists(data) is True
+ assert JSONPointer("/nosuchthing").exists(data) is False