In the spirit of default= parameter, a similar default_key= parameter

[kcrossen]

In the spirit of the dump/dumps default= parameter, a similar default_key= could be specified for
def _stringify_key(key):

For example, currently one may conveniently support UTC datetime as a dictionary value by:

def json_serial(obj):
    """JSON serializer for objects not serializable by default json code"""

    if isinstance(obj, datetime.datetime):
        serial = obj.isoformat()
        return serial
    raise TypeError("Type not serializable")

but _stringify_key fails when datetime is a dictionary key.

All of the same cautions would apply, of course, but at least someone who thought they knew what they were doing could get hurt their own way.

I hacked it w/

        elif _use_decimal and isinstance(key, Decimal):
            key = str(key)
        # kcrossen ...
        elif isinstance(key, datetime.datetime):
            key = key.isoformat()
        # ... kcrossen
        elif _skipkeys:
            key = None
        else:
            raise TypeError("key " + repr(key) + " is not a string")
        return key

but it doesn't feel righteous somehow.

[DeoLeung]

it will be great that we could provide customer parser to turn non-string keys into str, like numpy.int64 which is failing now

[kcrossen]

Can also be done to allow OrderedDict to remain ordered while usual dict is sorted:

        if (_item_sort_key and 
            # kcrossen ...
            (not isinstance(dct, OrderedDict))):
            # ... kcrossen
            items = []

approximately line 585 in encoder.py