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jsonpointer.py
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310 lines (216 loc) · 8.47 KB
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import copy
import re
from collections.abc import Mapping, Sequence
from itertools import tee, chain
_nothing = object()
def set_pointer(doc, pointer, value, inplace=True):
"""Resolves a pointer against doc and sets the value of the target within doc.
With inplace set to true, doc is modified as long as pointer is not the
root.
>>> obj = {'foo': {'anArray': [ {'prop': 44}], 'another prop': {'baz': 'A string' }}}
>>> set_pointer(obj, '/foo/anArray/0/prop', 55) == \
{'foo': {'another prop': {'baz': 'A string'}, 'anArray': [{'prop': 55}]}}
True
>>> set_pointer(obj, '/foo/yet another prop', 'added prop') == \
{'foo': {'another prop': {'baz': 'A string'}, 'yet another prop': 'added prop', 'anArray': [{'prop': 55}]}}
True
>>> obj = {'foo': {}}
>>> set_pointer(obj, '/foo/a%20b', 'x') == \
{'foo': {'a%20b': 'x' }}
True
"""
pointer = JsonPointer(pointer)
return pointer.set(doc, value, inplace)
def resolve_pointer(doc, pointer, default=_nothing):
"""Resolves pointer against doc and returns the referenced object
>>> obj = {'foo': {'anArray': [ {'prop': 44}], 'another prop': {'baz': 'A string' }}, 'a%20b': 1, 'c d': 2}
>>> resolve_pointer(obj, '') == obj
True
>>> resolve_pointer(obj, '/foo') == obj['foo']
True
>>> resolve_pointer(obj, '/foo/another prop') == obj['foo']['another prop']
True
>>> resolve_pointer(obj, '/foo/another prop/baz') == obj['foo']['another prop']['baz']
True
>>> resolve_pointer(obj, '/foo/anArray/0') == obj['foo']['anArray'][0]
True
>>> resolve_pointer(obj, '/some/path', None) == None
True
>>> resolve_pointer(obj, '/a b', None) == None
True
>>> resolve_pointer(obj, '/a%20b') == 1
True
>>> resolve_pointer(obj, '/c d') == 2
True
>>> resolve_pointer(obj, '/c%20d', None) == None
True
"""
pointer = JsonPointer(pointer)
return pointer.resolve(doc, default)
def pairwise(iterable):
"""Transforms a list to a list of tuples of adjacent items
s -> (s0,s1), (s1,s2), (s2, s3), ...
>>> list(pairwise([]))
[]
>>> list(pairwise([1]))
[]
>>> list(pairwise([1, 2, 3, 4]))
[(1, 2), (2, 3), (3, 4)]
"""
a, b = tee(iterable)
for _ in b:
break
return zip(a, b)
class JsonPointerException(Exception):
pass
class EndOfList(object):
"""Result of accessing element "-" of a list"""
def __init__(self, list_):
self.list_ = list_
def __repr__(self):
return "{cls}({lst})".format(cls=self.__class__.__name__, lst=repr(self.list_))
class JsonPointer(object):
"""A JSON Pointer that can reference parts of a JSON document"""
# Array indices must not contain:
# leading zeros, signs, spaces, decimals, etc
_RE_ARRAY_INDEX = re.compile("0|[1-9][0-9]*$")
_RE_INVALID_ESCAPE = re.compile("(~[^01]|~$)")
def __init__(self, pointer):
# validate escapes
invalid_escape = self._RE_INVALID_ESCAPE.search(pointer)
if invalid_escape:
raise JsonPointerException(
"Found invalid escape {}".format(invalid_escape.group())
)
parts = pointer.split("/")
if parts.pop(0) != "":
raise JsonPointerException("Location must start with /")
parts = [unescape(part) for part in parts]
self.parts = parts
def to_last(self, doc):
"""Resolves ptr until the last step, returns (sub-doc, last-step)"""
if not self.parts:
return doc, None
for part in self.parts[:-1]:
doc = self.walk(doc, part)
return doc, JsonPointer.get_part(doc, self.parts[-1])
def resolve(self, doc, default=_nothing):
"""Resolves the pointer against doc and returns the referenced object"""
for part in self.parts:
try:
doc = self.walk(doc, part)
except JsonPointerException:
if default is _nothing:
raise
else:
return default
return doc
get = resolve
def set(self, doc, value, inplace=True):
"""Resolve the pointer against the doc and replace the target with value."""
if len(self.parts) == 0:
if inplace:
raise JsonPointerException("Cannot set root in place")
return value
if not inplace:
doc = copy.deepcopy(doc)
(parent, part) = self.to_last(doc)
if isinstance(parent, Sequence) and part == "-":
parent.append(value)
else:
parent[part] = value
return doc
@classmethod
def get_part(cls, doc, part):
"""Returns the next step in the correct type"""
if isinstance(doc, Mapping):
return part
elif isinstance(doc, Sequence):
if part == "-":
return part
if not JsonPointer._RE_ARRAY_INDEX.match(str(part)):
raise JsonPointerException("'%s' is not a valid sequence index" % part)
return int(part)
elif hasattr(doc, "__getitem__"):
# Allow indexing via ducktyping
# if the target has defined __getitem__
return part
else:
raise JsonPointerException(
"Document '%s' does not support indexing, "
"must be mapping/sequence or support __getitem__" % type(doc)
)
def get_parts(self):
"""Returns the list of the parts. For example, JsonPointer('/a/b').get_parts() == ['a', 'b']"""
return self.parts
def walk(self, doc, part):
"""Walks one step in doc and returns the referenced part"""
part = JsonPointer.get_part(doc, part)
assert hasattr(doc, "__getitem__"), "invalid document type %s" % (type(doc),)
if isinstance(doc, Sequence):
if part == "-":
return EndOfList(doc)
try:
return doc[part]
except IndexError:
raise JsonPointerException("index '%s' is out of bounds" % (part,))
# Else the object is a mapping or supports __getitem__(so assume custom indexing)
try:
return doc[part]
except KeyError:
raise JsonPointerException("member '%s' not found in %s" % (part, doc))
def contains(self, ptr):
"""Returns True if self contains the given ptr"""
return self.parts[: len(ptr.parts)] == ptr.parts
def __contains__(self, item):
"""Returns True if self contains the given ptr"""
return self.contains(item)
def join(self, suffix):
"""Returns a new JsonPointer with the given suffix append to this ptr"""
if isinstance(suffix, JsonPointer):
suffix_parts = suffix.parts
elif isinstance(suffix, str):
suffix_parts = JsonPointer(suffix).parts
else:
suffix_parts = suffix
try:
return JsonPointer.from_parts(chain(self.parts, suffix_parts))
except: # noqa E722
raise JsonPointerException("Invalid suffix")
def __truediv__(self, suffix): # Python 3
return self.join(suffix)
@property
def path(self):
"""Returns the string representation of the pointer
>>> ptr = JsonPointer('/~0/0/~1').path == '/~0/0/~1'
"""
parts = [escape(part) for part in self.parts]
return "".join("/" + part for part in parts)
def __eq__(self, other):
"""Compares a pointer to another object
Pointers can be compared by comparing their strings (or splitted
strings), because no two different parts can point to the same
structure in an object (eg no different number representations)
"""
if not isinstance(other, JsonPointer):
return False
return self.parts == other.parts
def __hash__(self):
return hash(tuple(self.parts))
def __str__(self):
return self.path
def __repr__(self):
return type(self).__name__ + "(" + repr(self.path) + ")"
@classmethod
def from_parts(cls, parts):
"""Constructs a JsonPointer from a list of (unescaped) paths
>>> JsonPointer.from_parts(['a', '~', '/', 0]).path == '/a/~0/~1/0'
True
"""
parts = [escape(str(part)) for part in parts]
ptr = cls("".join("/" + part for part in parts))
return ptr
def escape(s):
return s.replace("~", "~0").replace("/", "~1")
def unescape(s):
return s.replace("~1", "/").replace("~0", "~")