A simple django template tag that lets you automatically render json from a python object

json_tags.py

"""
Usage:

{% load json_tags %}

var = myJsObject = {{ template_var|to_json }};

Features:

- Built in support for dates, datetimes, lazy translations.
- Safe escaping of script tags.
- Support for including QuryDict objects.
- Support for custom serialization methods on objects via defining a `to_json()` method.
"""

import datetime
import json
from decimal import Decimal
from django import template
from django.conf import settings
from django.http import QueryDict
from django.utils.encoding import force_str
from django.utils.functional import Promise
from django.utils.safestring import mark_safe

register = template.Library()

ISO_DATETIME_FORMAT = '%Y-%m-%dT%H:%M:%S.%fZ'


def json_handler(obj):
    if callable(getattr(obj, 'to_json', None)):
        return obj.to_json()
    elif isinstance(obj, datetime.datetime):
        return obj.strftime(ISO_DATETIME_FORMAT)
    elif isinstance(obj, datetime.date):
        return obj.isoformat()
    elif isinstance(obj, datetime.time):
        return obj.strftime('%H:%M:%S')
    elif isinstance(obj, Decimal):
        return float(obj)  # warning, potential loss of precision
    elif isinstance(obj, Promise):
        return force_str(obj)  # to support ugettext_lazy
    else:
        return json.JSONEncoder().default(obj)


@register.filter
def to_json(obj):
    def escape_script_tags(unsafe_str):
        # seriously: http://stackoverflow.com/a/1068548/8207
        return unsafe_str.replace('</script>', '<" + "/script>')

    # json.dumps does not properly convert QueryDict array parameter to json
    if isinstance(obj, QueryDict):
        obj = dict(obj)
    # apply formatting in debug mode for ease of development
    indent = None
    if settings.DEBUG:
        indent = 2
    return mark_safe(escape_script_tags(json.dumps(obj, default=json_handler, indent=indent)))

You can make it a tiny bit better with this:

    indent = None
    if settings.DEBUG:
        indent = 2
    return mark_safe(escape_script_tags(json.dumps(obj, default=json_handler, indent=indent)))

So that the JSON is minimal when in production and more readable when in DEBUG mode.

Thanks for the suggestion @mark0978 ! Updated.

Hello Cory Zue,
under which license do you offer this code snippet? Any easy permissive license?
Thanks in advance
Siegfried

sure, yeah do whatever you want with it! I don't know if a github comment is binding but feel free to consider it MIT

Thank you very much.
Siegfried

you need to import settings in order to use settings.debug in line 58.
from django.conf import settings

oops, thanks! fixed