A JSON decoder/encoder implementation for parsing dates as datetime objects in Python

DateTimeDecoder.py

#!/usr/bin/env python

# An example of decoding/encoding datetime values in JSON data in Python.
# Code adapted from: http://broadcast.oreilly.com/2009/05/pymotw-json.html

# Copyright (c) 2023, Abhinav Upadhyay
# 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.

# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "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 COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
# FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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# CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
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# OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.


from datetime import datetime
import json
from json import JSONDecoder
from json import JSONEncoder

obj = {'name':'foo', 'type': 'bar','date':datetime.now()}


class DateTimeDecoder(json.JSONDecoder):

    def __init__(self, *args, **kargs):
        JSONDecoder.__init__(self, object_hook=self.dict_to_object,
                             *args, **kargs)
    
    def dict_to_object(self, d): 
        if '__type__' not in d:
            return d

        type = d.pop('__type__')
        try:
            dateobj = datetime(**d)
            return dateobj
        except:
            d['__type__'] = type
            return d

class DateTimeEncoder(JSONEncoder):
    """ Instead of letting the default encoder convert datetime to string,
        convert datetime objects into a dict, which can be decoded by the
        DateTimeDecoder
    """
        
    def default(self, obj):
        if isinstance(obj, datetime):
            return {
                '__type__' : 'datetime',
                'year' : obj.year,
                'month' : obj.month,
                'day' : obj.day,
                'hour' : obj.hour,
                'minute' : obj.minute,
                'second' : obj.second,
                'microsecond' : obj.microsecond,
            }   
        else:
            return JSONEncoder.default(self, obj)

            
j = json.loads(json.dumps(obj,cls=DateTimeEncoder), cls=DateTimeDecoder)
print j['date']
print type(j['date'])

Thanks for this gist @abhinav-upadhyay, this is the best quick-summary of creating subclasses of JSONEncoders and JSONDecoders I've found yet!

Thanks. A beautiful implementation.

Hey genius, mind commenting all that code?

Thank you :) I finally got my object to successfully work with a datetime type :)

Thanks! Nice solution!

Can you give licence informations about this code please. I would like to use (and modify a bit) your code in my GPL application (not yet released).

The link http://broadcast.oreilly.com/2009/05/pymotw-json.html is not working anymore. Can you update it?
Could it be this one? https://doughellmann.com/blog/2009/05/24/pymotw-json/

See https://www.techatbloomberg.com/blog/work-dates-time-python/ for slight variation that preserves timezones.

Thanks. Same as @buhtz: a license would be welcome!

Thanks everyone on the feedback and positive comments. Added a 2 clause BSD license. I think it should work for everyone, whether they want to include it in commercial application or open source.

Thanks a lot!

I published your solution (with slight modifications) as a pypi package: https://pypi.org/project/datetimejson/.

Puh! Isn't this a bit to much to create a package for such a small piece of code?

Thanks @boileaum. I think the package is a convenience, I would use it myself next time I need this.

Puh! Isn't this a bit to much to create a package for such a small piece of code?

I agree but I have already 3 projects using it so I prefer to have it in a common package. Moreover, I am new to python packaging using github actions so it was a good exercise 🙂