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Bulletproof json.dump?

On 2020-07-06, Frank Millman <frank at> wrote:
> On 2020-07-06 2:06 PM, Jon Ribbens via Python-list wrote:
>> While I agree entirely with your point, there is however perhaps room
>> for a bit more helpfulness from the json module. There is no sensible
>> reason I can think of that it refuses to serialize sets, for example.
>> Going a bit further and, for example, automatically calling isoformat()
>> on date/time/datetime objects would perhaps be a bit more controversial,
>> but would frequently be useful, and there's no obvious downside that
>> occurs to me.
> I may be missing something, but that would cause a downside for me.
> I store Python lists and dicts in a database by calling dumps() when 
> saving them to the database and loads() when retrieving them.
> If a date was 'dumped' using isoformat(), then on retrieval I would not 
> know whether it was originally a string, which must remain as is, or was 
> originally a date object, which must be converted back to a date object.
> There is no perfect answer, but my solution works fairly well. When 
> dumping, I use 'default=repr'. This means that dates get dumped as 
> ', 7, 6)'. I look for that pattern on retrieval to 
> detect that it is actually a date object.

There is no difference whatsoever between matching on the repr output
you show above and matching on ISO-8601 datetimes, except that at least
ISO-8601 is an actual standard. So no, you haven't found a downside.