Check out this python library jsondiff , that will help you to identify the diff's

import json

import jsondiff

json1 = json.loads(
    '{"isDynamic": false, "name": "", "value": "SID:<sid>", "description": "instance","argsOrder": 1,"isMultiSelect": false}')

json2 = json.loads(
    '{ "name": "", "value": "SID:<sid>","isDynamic": false, "description": "instance","argsOrder": 1,"isMultiSelect": false}')

res = jsondiff.diff(json1, json2)
if res:
    print("Diff found")
else:
    print("Same")
Answer from Jenish on Stack Overflow
🌐
GitHub
github.com › xlwings › jsondiff
GitHub - xlwings/jsondiff: Diff JSON and JSON-like structures in Python · GitHub
Diff JSON and JSON-like structures in Python. Contribute to xlwings/jsondiff development by creating an account on GitHub.
Starred by 747 users
Forked by 89 users
Languages   Python
🌐
PyPI
pypi.org › project › jsondiff
jsondiff · PyPI
This will install the library and cli for jsondiff as well as its runtime dependencies. ... License: MIT License (The MIT License (MIT) Copyright (c) 2015 Zoomer Analytics LLC Permission is hereby granted, free o...) ... Download the file for your platform.
      » pip install jsondiff
    
Published   Aug 29, 2024
Version   2.2.1
Discussions

Multilevel JSON diff in python - Stack Overflow
Please link me to answer if this has already been answered, my problem is i want to get diff of multilevel json which is unordered. More on stackoverflow.com
🌐 stackoverflow.com
Diff two large JSON array or objects
Yes Firstly you have to load json data in python dictionary using json module/package After that jsondiff module/package help you check different This module/package also compare list,set,etc.👌 If will return empty dictionary {} if there is no different👍 import jsondiff oldJson = {1:"a",2:"b",3:"c"} newJson = {1:1,4:4} r = jsondiff.diff(oldJson,newJson) if r : print(r) else: print("404,No Different Found!") Output: {1: 1, 4: 4, delete: [2, 3]} 😀 json.diff take 1st arg oldJson means from which we are checking different & 2nd newJson. There are 3 syntax 🎲 : compact ( default ) Any Change in Value of key & new insrted key will display normaly symmetric Inserted & delete show differently change show normally explicit 👀 It is detailed Inserted Deleted Changed Show differently import jsondiff oldJson = {1:"a",2:"b",3:"c"} newJson = {1:1,4:4} r = jsondiff.diff(oldJson,newJson,syntax="explicit") if r: print(r) else: print("404,No Different Found!") Output : {insert: {4: 4}, update: {1: 1}, delete: [2, 3]} 😃 Finally 🔥,Now you doubt about how to access them You can access them using symbols eg. r[jsondiff.symbols.insert] OR from jsondiff import symbols r[symbols.insert] There are some other symbols which use in different compare like list,set, etc Note : if you try using insert in compact & update in compact & symmetric then you will get KeyError 😔 because those not exist there import jsondiff from jsondiff import symbols oldJson = {1:"a",2:"b",3:"c"} newJson = {1:1,4:4} r = jsondiff.diff(oldJson,newJson,syntax="explicit") if r: print("Deleted keys are ",r[symbols.delete]) else: print("404,No Different Found!") Output : Deleted keys are [2, 3] 🥳 Thanks for reading 😂 More on reddit.com
🌐 r/learnpython
3
3
February 26, 2022
python - Comparing two JSON objects irrespective of the sequence of elements in them - Stack Overflow
Is there any way / class / module in python to compare two json objects and print the changes/differences? I have tried with "json_tools" which is gives fairly good results, however diff failed i... More on stackoverflow.com
🌐 stackoverflow.com
python - Textually diffing JSON - Stack Overflow
I love JSON... I just think that would be easier. ... Why do you have to diff them textually? Wouldn't comparing the configuration data that they represent be more relevant (as well as easier)?. ... @martineau: I'm on the command line pulling the configs from the db/checked-in config files. If not textually, how do you suggest? ... Well, you could write a command line oriented Python ... More on stackoverflow.com
🌐 stackoverflow.com
🌐
PyPI
pypi.org › project › json-diff
json-diff · PyPI
Download the file for your platform. If you're not sure which to choose, learn more about installing packages. ... Details for the file json_diff-1.5.0.tar.gz.
      » pip install json-diff
    
Published   Aug 25, 2019
Version   1.5.0
🌐
SourceForge
sourceforge.net › projects › jsondiff.mirror
jsondiff download | SourceForge.net
August 29, 2024 - Download jsondiff for free. Diff JSON and JSON-like structures in Python. Diff JSON and JSON-like structures in Python.
Top answer
1 of 3
21

Check out this python library jsondiff , that will help you to identify the diff's

import json

import jsondiff

json1 = json.loads(
    '{"isDynamic": false, "name": "", "value": "SID:<sid>", "description": "instance","argsOrder": 1,"isMultiSelect": false}')

json2 = json.loads(
    '{ "name": "", "value": "SID:<sid>","isDynamic": false, "description": "instance","argsOrder": 1,"isMultiSelect": false}')

res = jsondiff.diff(json1, json2)
if res:
    print("Diff found")
else:
    print("Same")
2 of 3
6

UPDATED: See https://eggachecat.github.io/jycm-json-diff-viewer/ for a live demo! Now it has a JS-native implementation.

Affiliation: I am the author of this lib.

Yes! You can diff it with jycm which has a rendering tool out of the box.

It uses LCS, Edit distance and Kuhn–Munkres to diff arrays.

Here's an universal example with set in set and value changes in some set

from jycm.helper import make_ignore_order_func
from jycm.jycm import YouchamaJsonDiffer

left = {
    "set_in_set": [
        {
            "id": 1,
            "label": "label:1",
            "set": [
                1,
                5,
                3
            ]
        },
        {
            "id": 2,
            "label": "label:2",
            "set": [
                4,
                5,
                6
            ]
        }
    ]
}

right = {
    "set_in_set": [
        {
            "id": 2,
            "label": "label:2",
            "set": [
                6,
                5,
                4
            ]
        },
        {
            "id": 1,
            "label": "label:1111",
            "set": [
                3,
                2,
                1
            ]
        }
    ]
}

ycm = YouchamaJsonDiffer(left, right, ignore_order_func=make_ignore_order_func([
    "^set_in_set$",
    "^set_in_set->\\[\\d+\\]->set$"
]))

ycm.diff()

expected = {
    'list:add': [
        {'left': '__NON_EXIST__', 'right': 2, 'left_path': '', 'right_path': 'set_in_set->[1]->set->[1]'}
    ],
    'list:remove': [
        {'left': 5, 'right': '__NON_EXIST__', 'left_path': 'set_in_set->[0]->set->[1]', 'right_path': ''}
    ],
    'value_changes': [
        {'left': 'label:1', 'right': 'label:1111', 'left_path': 'set_in_set->[0]->label',
         'right_path': 'set_in_set->[1]->label', 'old': 'label:1', 'new': 'label:1111'}
    ]
}

assert ycm.to_dict(no_pairs=True) == expected

you can set no_pairs=False to get the all pairs. Here's a rendered example:

As for the example here, you can use it as:

from jycm.helper import make_ignore_order_func
from jycm.jycm import YouchamaJsonDiffer

left = {
    "data": [{"x": 1, "y": 2}, {"x": 3, "y": 4}]
}

right = {
    "data": [{"x": 3, "y": 4}, {"x": 1, "y": 2}]
}

ycm = YouchamaJsonDiffer(left, right, ignore_order_func=make_ignore_order_func([
    "^data",
]))

ycm.diff()

assert ycm.to_dict(no_pairs=True) == {}

Bonus, you the values are interrupted as coordinates on plain, you can even define a operator to determine whether two points should be matched!(Then comparing their values)

Here's the code:

from typing import Tuple

from jycm.helper import make_ignore_order_func
from jycm.jycm import YouchamaJsonDiffer
from jycm.operator import BaseOperator
import math

left = {
    "data": [
        {"x": 1, "y": 1},
        {"x": 10, "y": 10},
        {"x": 100, "y": 100}
    ]
}

right = {
    "data": [
        {"x": 150, "y": 150},
        {"x": 10, "y": 11},
        {"x": 2, "y": 3}
    ]
}


class L2DistanceOperator(BaseOperator):
    __operator_name__ = "operator:l2distance"
    __event__ = "operator:l2distance"

    def __init__(self, path_regex, distance_threshold):
        super().__init__(path_regex=path_regex)
        self.distance_threshold = distance_threshold

    def diff(self, level: 'TreeLevel', instance, drill: bool) -> Tuple[bool, float]:
        distance = math.sqrt(
            (level.left["x"] - level.right["x"]) ** 2 + (level.left["y"] - level.right["y"]) ** 2
        )
        info = {
            "distance": distance,
            "distance_threshold": self.distance_threshold,
            "pass": distance < self.distance_threshold
        }

        if not drill:
            instance.report(self.__event__, level, info)
            return False, 1 if info["pass"] else 0
        return True, 1 if info["pass"] else 0


ycm = YouchamaJsonDiffer(left, right, ignore_order_func=make_ignore_order_func([
    "^data$",
]), custom_operators=[
    L2DistanceOperator("^data->\\[.*\\]$", 10),
])

ycm.diff()

expected = {
    'just4vis:pairs': [
        {'left': 1, 'right': 2, 'left_path': 'data->[0]->x', 'right_path': 'data->[2]->x'},
        {'left': {'x': 1, 'y': 1}, 'right': {'x': 2, 'y': 3}, 'left_path': 'data->[0]',
         'right_path': 'data->[2]'},
        {'left': 1, 'right': 3, 'left_path': 'data->[0]->y', 'right_path': 'data->[2]->y'},
        {'left': {'x': 1, 'y': 1}, 'right': {'x': 2, 'y': 3}, 'left_path': 'data->[0]',
         'right_path': 'data->[2]'},
        {'left': {'x': 1, 'y': 1}, 'right': {'x': 2, 'y': 3}, 'left_path': 'data->[0]',
         'right_path': 'data->[2]'}
    ],
    'list:add': [
        {'left': '__NON_EXIST__', 'right': {'x': 150, 'y': 150}, 'left_path': '', 'right_path': 'data->[0]'}
    ],
    'list:remove': [
        {'left': {'x': 100, 'y': 100}, 'right': '__NON_EXIST__', 'left_path': 'data->[2]', 'right_path': ''}
    ],
    'operator:l2distance': [
        {'left': {'x': 1, 'y': 1}, 'right': {'x': 2, 'y': 3}, 'left_path': 'data->[0]',
         'right_path': 'data->[2]', 'distance': 2.23606797749979, 'distance_threshold': 10,
         'pass': True},
        {'left': {'x': 10, 'y': 10}, 'right': {'x': 10, 'y': 11}, 'left_path': 'data->[1]',
         'right_path': 'data->[1]', 'distance': 1.0, 'distance_threshold': 10,
         'pass': True}
    ],
    'value_changes': [
        {'left': 1, 'right': 2, 'left_path': 'data->[0]->x', 'right_path': 'data->[2]->x', 'old': 1, 'new': 2},
        {'left': 1, 'right': 3, 'left_path': 'data->[0]->y', 'right_path': 'data->[2]->y', 'old': 1, 'new': 3},
        {'left': 10, 'right': 11, 'left_path': 'data->[1]->y', 'right_path': 'data->[1]->y', 'old': 10, 'new': 11}
    ]
}
assert ycm.to_dict() == expected

As you can see jycm report addition and remove for points {'x': 150, 'y': 150} and {'x': 100, 'y': 100} for their distances are too far (more than 10) and value-change for the other two points.

P.S. RENDERER DEMO

🌐
JSON Diff
jsondiff.com
JSON Diff - The semantic JSON compare tool
Validate, format, and compare two JSON documents. See the differences between the objects instead of just the new lines and mixed up properties.
🌐
PyPI
pypi.org › project › jsoncomparison
jsoncomparison · PyPI
Details for the file jsoncomparison-1.1.0-py3-none-any.whl. Download URL: jsoncomparison-1.1.0-py3-none-any.whl
      » pip install jsoncomparison
    
Published   May 17, 2021
Version   1.1.0
Find elsewhere
🌐
Reddit
reddit.com › r/learnpython › diff two large json array or objects
r/learnpython on Reddit: Diff two large JSON array or objects
February 26, 2022 -

I have a Python lambda function downloading a large excel file and converting it to JSON.

This file will be downloaded at least once a day (as the data can change)

I need to push the changed/updated data to an API.

Is there a way for me to compare two JSON files and output the diff?

It would be perfect if it would output multiple arrays of objects.

1 array of objects that have changed (I don’t care what has changed, just need to know that it has)

1 array of removed/deleted objects.

Top answer
1 of 1
4
Yes Firstly you have to load json data in python dictionary using json module/package After that jsondiff module/package help you check different This module/package also compare list,set,etc.👌 If will return empty dictionary {} if there is no different👍 import jsondiff oldJson = {1:"a",2:"b",3:"c"} newJson = {1:1,4:4} r = jsondiff.diff(oldJson,newJson) if r : print(r) else: print("404,No Different Found!") Output: {1: 1, 4: 4, delete: [2, 3]} 😀 json.diff take 1st arg oldJson means from which we are checking different & 2nd newJson. There are 3 syntax 🎲 : compact ( default ) Any Change in Value of key & new insrted key will display normaly symmetric Inserted & delete show differently change show normally explicit 👀 It is detailed Inserted Deleted Changed Show differently import jsondiff oldJson = {1:"a",2:"b",3:"c"} newJson = {1:1,4:4} r = jsondiff.diff(oldJson,newJson,syntax="explicit") if r: print(r) else: print("404,No Different Found!") Output : {insert: {4: 4}, update: {1: 1}, delete: [2, 3]} 😃 Finally 🔥,Now you doubt about how to access them You can access them using symbols eg. r[jsondiff.symbols.insert] OR from jsondiff import symbols r[symbols.insert] There are some other symbols which use in different compare like list,set, etc Note : if you try using insert in compact & update in compact & symmetric then you will get KeyError 😔 because those not exist there import jsondiff from jsondiff import symbols oldJson = {1:"a",2:"b",3:"c"} newJson = {1:1,4:4} r = jsondiff.diff(oldJson,newJson,syntax="explicit") if r: print("Deleted keys are ",r[symbols.delete]) else: print("404,No Different Found!") Output : Deleted keys are [2, 3] 🥳 Thanks for reading 😂
🌐
GitHub
github.com › cpatrickalves › json-diff
GitHub - cpatrickalves/json-diff: A Python script that compares two JSON files and shows their differences.
#> python json_diffs.py examples\file01.json examples\file02.json The values in object ID are different: SGML != SL The values in object GlossTerm are different: Standard Generalized Markup Language != Standard Generalized Language The values in object Abbrev are different: ISO 8879:1986 != ISO 8559:1986 The values in object GlossSeeAlso are different: ['GML', 'XML'] != ['JSO', 'XML'] The data is different
Author   cpatrickalves
🌐
PyPI
pypi.org › project › deepdiff
deepdiff · PyPI
Download the file for your platform.
      » pip install deepdiff
    
Published   Mar 18, 2026
Version   8.6.2
🌐
PyPI
pypi.org › project › custom-json-diff
custom-json-diff · PyPI
Uploaded Mar 12, 2025 Python 3 · Details for the file custom_json_diff-2.1.6.tar.gz. Download URL: custom_json_diff-2.1.6.tar.gz · Upload date: Mar 12, 2025 · Size: 40.7 kB · Tags: Source · Uploaded using Trusted Publishing? Yes · Uploaded via: twine/6.1.0 CPython/3.12.9 ·
      » pip install custom-json-diff
    
Published   Mar 12, 2025
Version   2.1.6
🌐
PyPI
pypi.org › project › json-differ
json-differ · PyPI
json-differ examples/sample1.json examples/sample2.json · Sample input files are included in examples/. ✅ No dependencies ✅ Nested dict & list comparison ✅ CLI + Python API both supported ✅ Simple structured output ... Built with ❤️ for developers who appreciate small, smart tools. ... Download the file for your platform.
      » pip install json-differ
    
Published   Oct 20, 2025
Version   1.0.0
🌐
Delft Stack
delftstack.com › home › howto › python › python json diff
How to Compare Multilevel JSON Objects Using JSON Diff in Python | Delft Stack
February 2, 2024 - Using this library, it can become pretty easy to find differences between JSON objects, be they multi-leveled or unordered. Before jumping to see how we can do so, let’s first install jsondiff since it’s a third-party module and does not come built-in with any standard Python installation. Open the command prompt and execute the below command to start installing jsondiff: ... Collecting jsondiff Downloading jsondiff-2.0.0-py3-none-any.whl (6.6 kB) Installing collected packages: jsondiff Successfully installed jsondiff-2.0.0
🌐
pytz
pythonhosted.org › opslib › icsutils › jsondiff.html
IcsUtils.JsonDiff Common Library — OpsLib Library alpha documentation
>>> from opslib.icsutils.jsondiff import Comparator >>> import json >>> old_json = { ... "name": "opslib", ... "version": "1.2.0", ... "members": { ... "role": "ops", ... "group": [ "ops", "devops" ] ... } ... } >>> new_json = { ... "name": "opslib", ... "version": "1.3.0", ...
🌐
Deviloper's Blog
deviloper.in › advanced-json-diff-checker-in-python-an-in-depth-guide
Advanced JSON Diff Checker in Python: An In-Depth Guide
September 9, 2024 - The deepdiff library is a powerful tool for comparing complex data structures in Python, including JSON objects. It provides a comprehensive set of functionalities to identify differences between two data structures, making it perfect for our JSON diff checker.
🌐
PyPI
pypi.org › project › json-files-compare
json-files-compare · PyPI
February 5, 2023 - Details for the file json_files_compare-1.0.1-py3-none-any.whl. Download URL: json_files_compare-1.0.1-py3-none-any.whl
      » pip install json-files-compare
    
Published   Feb 05, 2023
Version   1.0.1
🌐
GitHub
github.com › parjun8840 › jsondiff
GitHub - parjun8840/jsondiff: Json diff using python
C:\Users\parjun8840\eclipse-workspace\PythonDev>python jsondiff.py --help usage: jsondiff.py [-h] [-f1 FILE1_PATH] [-f2 FILE2_PATH] JSON DIFF optional arguments: -h, --help show this help message and exit -f1 FILE1_PATH, --FILE1_PATH FILE1_PATH First Json File -f2 FILE2_PATH, --FILE2_PATH FILE2_PATH Second Json file C:\Users\parjun8840\eclipse-workspace\PythonDev> Scenario 1: Both files same content Input files used: json_dict1 ,json_dict1 have same content {"test1": "1", "test2" : "2", "test3" : "abcd", "test4" : "xyz", "test5" : "12ab", "test6" : "12ab" } C:\Users\parjun8840\eclipse-workspace\PythonDev>python jsondiff.py -f1 json_dict1 -f2 json_dict2 INFO: Files exists and non-empty JSON files are same C:\Users\parjun8840\eclipse-workspace\PythonDev> Scenario 2: When one of the file has extra key and other one has different value for the same key.
Author   parjun8840
Top answer
1 of 6
22

If any of your tool has the option, Patience Diff could work a lot better for you. I'll try to find a tool with it (other tha Git and Bazaar) and report back.

Edit: It seems that the implementation in Bazaar is usable as a standalone tool with minimal changes.

Edit2: WTH, why not paste the source of the new cool diff script you made me hack? Here it is, no copyright claim on my side, it's just Bram/Canonical's code re-arranged.

#!/usr/bin/env python
# Copyright (C) 2005, 2006, 2007 Canonical Ltd
# Copyright (C) 2005 Bram Cohen, Copyright (C) 2005, 2006 Canonical Ltd
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program; if not, write to the Free Software
# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA


import os
import sys
import time
import difflib
from bisect import bisect

__all__ = ['PatienceSequenceMatcher', 'unified_diff', 'unified_diff_files']

py3k = False
try:
    xrange
except NameError:
    py3k = True
    xrange = range

# This is a version of unified_diff which only adds a factory parameter
# so that you can override the default SequenceMatcher
# this has been submitted as a patch to python
def unified_diff(a, b, fromfile='', tofile='', fromfiledate='',
                 tofiledate='', n=3, lineterm='\n',
                 sequencematcher=None):
    r"""
    Compare two sequences of lines; generate the delta as a unified diff.

    Unified diffs are a compact way of showing line changes and a few
    lines of context.  The number of context lines is set by 'n' which
    defaults to three.

    By default, the diff control lines (those with ---, +++, or @@) are
    created with a trailing newline.  This is helpful so that inputs
    created from file.readlines() result in diffs that are suitable for
    file.writelines() since both the inputs and outputs have trailing
    newlines.

    For inputs that do not have trailing newlines, set the lineterm
    argument to "" so that the output will be uniformly newline free.

    The unidiff format normally has a header for filenames and modification
    times.  Any or all of these may be specified using strings for
    'fromfile', 'tofile', 'fromfiledate', and 'tofiledate'.  The modification
    times are normally expressed in the format returned by time.ctime().

    Example:

    >>> for line in unified_diff('one two three four'.split(),
    ...             'zero one tree four'.split(), 'Original', 'Current',
    ...             'Sat Jan 26 23:30:50 1991', 'Fri Jun 06 10:20:52 2003',
    ...             lineterm=''):
    ...     print line
    --- Original Sat Jan 26 23:30:50 1991
    +++ Current Fri Jun 06 10:20:52 2003
    @@ -1,4 +1,4 @@
    +zero
     one
    -two
    -three
    +tree
     four
    """
    if sequencematcher is None:
        import difflib
        sequencematcher = difflib.SequenceMatcher

    if fromfiledate:
        fromfiledate = '\t' + str(fromfiledate)
    if tofiledate:
        tofiledate = '\t' + str(tofiledate)

    started = False
    for group in sequencematcher(None,a,b).get_grouped_opcodes(n):
        if not started:
            yield '--- %s%s%s' % (fromfile, fromfiledate, lineterm)
            yield '+++ %s%s%s' % (tofile, tofiledate, lineterm)
            started = True
        i1, i2, j1, j2 = group[0][3], group[-1][4], group[0][5], group[-1][6]
        yield "@@ -%d,%d +%d,%d @@%s" % (i1+1, i2-i1, j1+1, j2-j1, lineterm)
        for tag, i1, i2, j1, j2 in group:
            if tag == 'equal':
                for line in a[i1:i2]:
                    yield ' ' + line
                continue
            if tag == 'replace' or tag == 'delete':
                for line in a[i1:i2]:
                    yield '-' + line
            if tag == 'replace' or tag == 'insert':
                for line in b[j1:j2]:
                    yield '+' + line


def unified_diff_files(a, b, sequencematcher=None):
    """Generate the diff for two files.
    """
    mode = 'rb'
    if py3k: mode = 'r'
    # Should this actually be an error?
    if a == b:
        return []
    if a == '-':
        file_a = sys.stdin
        time_a = time.time()
    else:
        file_a = open(a, mode)
        time_a = os.stat(a).st_mtime

    if b == '-':
        file_b = sys.stdin
        time_b = time.time()
    else:
        file_b = open(b, mode)
        time_b = os.stat(b).st_mtime

    # TODO: Include fromfiledate and tofiledate
    return unified_diff(file_a.readlines(), file_b.readlines(),
                        fromfile=a, tofile=b,
                        sequencematcher=sequencematcher)


def unique_lcs_py(a, b):
    """Find the longest common subset for unique lines.

    :param a: An indexable object (such as string or list of strings)
    :param b: Another indexable object (such as string or list of strings)
    :return: A list of tuples, one for each line which is matched.
            [(line_in_a, line_in_b), ...]

    This only matches lines which are unique on both sides.
    This helps prevent common lines from over influencing match
    results.
    The longest common subset uses the Patience Sorting algorithm:
    http://en.wikipedia.org/wiki/Patience_sorting
    """
    # set index[line in a] = position of line in a unless
    # a is a duplicate, in which case it's set to None
    index = {}
    for i in xrange(len(a)):
        line = a[i]
        if line in index:
            index[line] = None
        else:
            index[line]= i
    # make btoa[i] = position of line i in a, unless
    # that line doesn't occur exactly once in both,
    # in which case it's set to None
    btoa = [None] * len(b)
    index2 = {}
    for pos, line in enumerate(b):
        next = index.get(line)
        if next is not None:
            if line in index2:
                # unset the previous mapping, which we now know to
                # be invalid because the line isn't unique
                btoa[index2[line]] = None
                del index[line]
            else:
                index2[line] = pos
                btoa[pos] = next
    # this is the Patience sorting algorithm
    # see http://en.wikipedia.org/wiki/Patience_sorting
    backpointers = [None] * len(b)
    stacks = []
    lasts = []
    k = 0
    for bpos, apos in enumerate(btoa):
        if apos is None:
            continue
        # as an optimization, check if the next line comes at the end,
        # because it usually does
        if stacks and stacks[-1] < apos:
            k = len(stacks)
        # as an optimization, check if the next line comes right after
        # the previous line, because usually it does
        elif stacks and stacks[k] < apos and (k == len(stacks) - 1 or
                                              stacks[k+1] > apos):
            k += 1
        else:
            k = bisect(stacks, apos)
        if k > 0:
            backpointers[bpos] = lasts[k-1]
        if k < len(stacks):
            stacks[k] = apos
            lasts[k] = bpos
        else:
            stacks.append(apos)
            lasts.append(bpos)
    if len(lasts) == 0:
        return []
    result = []
    k = lasts[-1]
    while k is not None:
        result.append((btoa[k], k))
        k = backpointers[k]
    result.reverse()
    return result


def recurse_matches_py(a, b, alo, blo, ahi, bhi, answer, maxrecursion):
    """Find all of the matching text in the lines of a and b.

    :param a: A sequence
    :param b: Another sequence
    :param alo: The start location of a to check, typically 0
    :param ahi: The start location of b to check, typically 0
    :param ahi: The maximum length of a to check, typically len(a)
    :param bhi: The maximum length of b to check, typically len(b)
    :param answer: The return array. Will be filled with tuples
                   indicating [(line_in_a, line_in_b)]
    :param maxrecursion: The maximum depth to recurse.
                         Must be a positive integer.
    :return: None, the return value is in the parameter answer, which
             should be a list

    """
    if maxrecursion < 0:
        print('max recursion depth reached')
        # this will never happen normally, this check is to prevent DOS attacks
        return
    oldlength = len(answer)
    if alo == ahi or blo == bhi:
        return
    last_a_pos = alo-1
    last_b_pos = blo-1
    for apos, bpos in unique_lcs_py(a[alo:ahi], b[blo:bhi]):
        # recurse between lines which are unique in each file and match
        apos += alo
        bpos += blo
        # Most of the time, you will have a sequence of similar entries
        if last_a_pos+1 != apos or last_b_pos+1 != bpos:
            recurse_matches_py(a, b, last_a_pos+1, last_b_pos+1,
                apos, bpos, answer, maxrecursion - 1)
        last_a_pos = apos
        last_b_pos = bpos
        answer.append((apos, bpos))
    if len(answer) > oldlength:
        # find matches between the last match and the end
        recurse_matches_py(a, b, last_a_pos+1, last_b_pos+1,
                           ahi, bhi, answer, maxrecursion - 1)
    elif a[alo] == b[blo]:
        # find matching lines at the very beginning
        while alo < ahi and blo < bhi and a[alo] == b[blo]:
            answer.append((alo, blo))
            alo += 1
            blo += 1
        recurse_matches_py(a, b, alo, blo,
                           ahi, bhi, answer, maxrecursion - 1)
    elif a[ahi - 1] == b[bhi - 1]:
        # find matching lines at the very end
        nahi = ahi - 1
        nbhi = bhi - 1
        while nahi > alo and nbhi > blo and a[nahi - 1] == b[nbhi - 1]:
            nahi -= 1
            nbhi -= 1
        recurse_matches_py(a, b, last_a_pos+1, last_b_pos+1,
                           nahi, nbhi, answer, maxrecursion - 1)
        for i in xrange(ahi - nahi):
            answer.append((nahi + i, nbhi + i))


def _collapse_sequences(matches):
    """Find sequences of lines.

    Given a sequence of [(line_in_a, line_in_b),]
    find regions where they both increment at the same time
    """
    answer = []
    start_a = start_b = None
    length = 0
    for i_a, i_b in matches:
        if (start_a is not None
            and (i_a == start_a + length)
            and (i_b == start_b + length)):
            length += 1
        else:
            if start_a is not None:
                answer.append((start_a, start_b, length))
            start_a = i_a
            start_b = i_b
            length = 1

    if length != 0:
        answer.append((start_a, start_b, length))

    return answer


def _check_consistency(answer):
    # For consistency sake, make sure all matches are only increasing
    next_a = -1
    next_b = -1
    for (a, b, match_len) in answer:
        if a < next_a:
            raise ValueError('Non increasing matches for a')
        if b < next_b:
            raise ValueError('Non increasing matches for b')
        next_a = a + match_len
        next_b = b + match_len


class PatienceSequenceMatcher_py(difflib.SequenceMatcher):
    """Compare a pair of sequences using longest common subset."""

    _do_check_consistency = True

    def __init__(self, isjunk=None, a='', b=''):
        if isjunk is not None:
            raise NotImplementedError('Currently we do not support'
                                      ' isjunk for sequence matching')
        difflib.SequenceMatcher.__init__(self, isjunk, a, b)

    def get_matching_blocks(self):
        """Return list of triples describing matching subsequences.

        Each triple is of the form (i, j, n), and means that
        a[i:i+n] == b[j:j+n].  The triples are monotonically increasing in
        i and in j.

        The last triple is a dummy, (len(a), len(b), 0), and is the only
        triple with n==0.

        >>> s = PatienceSequenceMatcher(None, "abxcd", "abcd")
        >>> s.get_matching_blocks()
        [(0, 0, 2), (3, 2, 2), (5, 4, 0)]
        """
        # jam 20060525 This is the python 2.4.1 difflib get_matching_blocks
        # implementation which uses __helper. 2.4.3 got rid of helper for
        # doing it inline with a queue.
        # We should consider doing the same for recurse_matches

        if self.matching_blocks is not None:
            return self.matching_blocks

        matches = []
        recurse_matches_py(self.a, self.b, 0, 0,
                           len(self.a), len(self.b), matches, 10)
        # Matches now has individual line pairs of
        # line A matches line B, at the given offsets
        self.matching_blocks = _collapse_sequences(matches)
        self.matching_blocks.append( (len(self.a), len(self.b), 0) )
        if PatienceSequenceMatcher_py._do_check_consistency:
            if __debug__:
                _check_consistency(self.matching_blocks)

        return self.matching_blocks


unique_lcs = unique_lcs_py
recurse_matches = recurse_matches_py
PatienceSequenceMatcher = PatienceSequenceMatcher_py


def main(args):
    import optparse
    p = optparse.OptionParser(usage='%prog [options] file_a file_b'
                                    '\nFiles can be "-" to read from stdin')
    p.add_option('--patience', dest='matcher', action='store_const', const='patience',
                 default='patience', help='Use the patience difference algorithm')
    p.add_option('--difflib', dest='matcher', action='store_const', const='difflib',
                 default='patience', help='Use python\'s difflib algorithm')

    algorithms = {'patience':PatienceSequenceMatcher, 'difflib':difflib.SequenceMatcher}

    (opts, args) = p.parse_args(args)
    matcher = algorithms[opts.matcher]

    if len(args) != 2:
        print('You must supply 2 filenames to diff')
        return -1

    for line in unified_diff_files(args[0], args[1], sequencematcher=matcher):
        sys.stdout.write(line)


if __name__ == '__main__':
    sys.exit(main(sys.argv[1:]))

Edit 3: I've also made a minimally standalone version of Neil Fraser's Diff Match and Patch, I'd be very interested in a comparison of results for your use case. Again, I claim no copyrights.

Edit 4: I just found DataDiff, which might be another tool to try.

DataDiff is a library to provide human-readable diffs of python data structures. It can handle sequence types (lists, tuples, etc), sets, and dictionaries.

Dictionaries and sequences will be diffed recursively, when applicable.

2 of 6
4

So, I wrote a tool to do unified diffs of JSON files a while ago that might be of some interest.

https://github.com/jclulow/jsondiff

Some examples of input and output for the tool appear on the github page.