JSON Dotted Read Access

Simplify access to JSON structures by introduce a dotted access notation.

The intended use case is to read JSON data once. The use is not limited to JSON data. All data in a top-level dictionary can be accessed. Use dictionaries and lists to structure these data. The data - the leafs in this data tree - can be all kind of Python objects.

Limitations

no dots (.) in keys allowed
read-only structure - no modifications (update/refresh) possible
no caching implemented

Supported and tested Python versions

Python 2.7, tested with 2.7.17
Python 3, tested with 3.8.1

Requirements

There are no additional requirements. All you need is Python.

Installation

No installation is necessary. Add the file JsonDottedReadAccess.py to your project and use it. Alternatively copy the whole directory and treat it as package.

Usage

Convert JSON string to a Python object

This step is optional. You can use a Python object directly.

import json
districts = """
{
    "cities":{
        "Dresden":[
            "Altstadt",
            "Blasewitz",
            "Cotta",
            "Klotzsche",
            "Leuben", 
            "..."
        ],
        "Chemnitz":[
            "Adelsberg",
            "Altchemnitz",
            "Altendorf",
            "Bernsdorf",
            "Borna-Heinersdorf",
            "..."
        ]
    }
}
"""

pyobj = json.loads(districts.strip())

Create object for dotted access

from JsonDottedReadAccess import JsonDottedReadAccess
j = JsonDottedReadAccess(pyobj)

Access methods

`get(self, key, failobj=None)`

get(key) returns fallback object, if the item doesn't exist.

`getitem(self, key)`

[key] raises KeyError or IndexError exceptions during access to non-existing items.

Access elements

The individual elements are accessed via the description of the path, whereby the successive levels are connected by dots (".").

Access dictionary elements via keys and list elements via the numerical index.

Access pattern:

cities = j.get("cities")
cities = j["cities"]

non_existing_city = j.get("cities.non-existing", 42)

destricts = j.get("cities.Dresden")
destrict = j["cities.Dresden.2"]
non_existing_destrict = j.get("cities.Dresden.non-existing", 42)

More examples are shown on the section "Examples".

Examples

Basic Example: Access JSON data

import json
from JsonDottedReadAccess import JsonDottedReadAccess

districts = """
{
    "cities":{
        "Dresden":[
            "Altstadt",
            "Blasewitz",
            "Cotta",
            "Klotzsche",
            "Leuben",
            "..."
        ],
        "Chemnitz":[
            "Adelsberg",
            "Altchemnitz",
            "Altendorf",
            "Bernsdorf",
            "Borna-Heinersdorf",
            "..."
        ]
    }
}
"""

pyobj = json.loads(districts.strip())
j = JsonDottedReadAccess(pyobj)

print(j.get("cities"))
{u'Dresden': [u'Altstadt', u'Blasewitz', u'Cotta', u'Klotzsche', u'Leuben', u'...'], u'Chemnitz': [u'Adelsberg', u'Altchemnitz', u'Altendorf', u'Bernsdorf', u'Borna-Heinersdorf', u'...']}

print( j.get("cities.Dresden"))
[u'Altstadt', u'Blasewitz', u'Cotta', u'Klotzsche', u'Leuben', u'...']

print(j.get("cities.Dresden.3"))
Klotzsche

Complex Example

from JsonDottedReadAccess import JsonDottedReadAccess

d = {'level1': {'level2-a': None,
                'level2-b': [{'level3-b': 1}],
                'level2-c': {'level3-c': 1},
                'level2-d': 'level3-d'}}
j = JsonDottedReadAccess(d)

print(j.get('level1'))
{'level2-c': {'level3-c': 1}, 'level2-b': [{'level3-b': 1}], 'level2-a': None, 'level2-d': 'level3-d'}

print(j['level1.level2-b'])
[{'level3-b': 1}]

print(j.get('level1.level2-d'))
'level3-d'

print(j.get('level1.nonexisting'))
None

print(j['level1.nonexisting'])
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "JsonDottedReadAccess.py", line 58, in __getitem__
    val = val[key]
KeyError: 'nonexisting'

Changelog

April 2020

Add init.py to use it as package

March 2020

Extend documentation

January 2020

Extend tests
get() catches IndexError and returns failobj instead
Add Python3 compatibility

November 2017

Initial version

Project page and feedback

The project page is at https://www.carstengrohmann.de/jsondottedreadaccess.html.

The source code is at https://sr.ht/~carstengrohmann/JsonDottedReadAccess.

Comments, suggestions and patches are welcome and appreciated. Please email me.

License

This software is covered by the MIT License.

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.