path: root/jsonpointer.py

# -*- coding: utf-8 -*-
#
# python-json-pointer - An implementation of the JSON Pointer syntax
# https://github.com/stefankoegl/python-json-pointer
#
# 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.
#

""" Identify specific nodes in a JSON document (RFC 6901) """

# Will be parsed by setup.py to determine package metadata
__author__ = u'Stefan Kögl <stefan@skoegl.net>'
__version__ = u'1.0'
__website__ = u'https://github.com/stefankoegl/python-json-pointer'
__license__ = u'Modified BSD License'


try:
    from urllib import unquote
    from itertools import izip
except ImportError: # Python 3
    from urllib.parse import unquote
    izip = zip

from itertools import tee
import re


# array indices must not contain leading zeros, signs, spaces, decimals, etc
RE_ARRAY_INDEX=re.compile('0|[1-9][0-9]*$')


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_))


_nothing = object()


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" }}}

    >>> resolve_pointer(obj, '') == obj
    True

    >>> resolve_pointer(obj, '/foo') == obj['foo']
    True

    >>> resolve_pointer(obj, '/foo/another%20prop') == obj['foo']['another prop']
    True

    >>> resolve_pointer(obj, '/foo/another%20prop/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

    """

    pointer = JsonPointer(pointer)
    return pointer.resolve(doc, default)


class JsonPointer(object):
    """ A JSON Pointer that can reference parts of an JSON document """

    def __init__(self, pointer):
        parts = pointer.split('/')
        if parts.pop(0) != '':
            raise JsonPointerException('location must starts with /')

        parts = map(unquote, parts)
        parts = [part.replace('~1', '/') for part in parts]
        parts = [part.replace('~0', '~') for part in parts]
        self.parts = parts


    def to_last(self, doc, default=_nothing):
        """ 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, self.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 get_part(self, doc, part):
        """ Returns the next step in the correct type """

        if isinstance(doc, dict):
            return part

        elif isinstance(doc, list):

            if part == '-':
                return part

            if not RE_ARRAY_INDEX.match(str(part)):
                raise JsonPointerException("'%s' is not a valid list index" % (part, ))

            return int(part)

        else:
            raise JsonPointerException("Unknown document type '%s'" % (doc.__class__,))


    def walk(self, doc, part):
        """ Walks one step in doc and returns the referenced part """

        part = self.get_part(doc, part)

        if isinstance(doc, dict):
            try:
                return doc[part]

            except KeyError:
                raise JsonPointerException("member '%s' not found in %s" % (part, doc))

        elif isinstance(doc, list):

            if part == '-':
                return EndOfList(doc)

            try:
                return doc[part]

            except IndexError:
                raise JsonPointerException("index '%s' is out of bounds" % (part, ))


        else:
            raise JsonPointerException("can not go beyond '%s' (type '%s')" % (part, doc.__class__))



    def contains(self, ptr):
        """" Returns True if self contains the given ptr """
        return len(self.parts) > len(ptr.parts) and \
             self.parts[:len(ptr.parts)] == ptr.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 pairwise(iterable):
    "s -> (s0,s1), (s1,s2), (s2, s3), ..."
    a, b = tee(iterable)
    for _ in b:
        break
    return izip(a, b)