Date, time and datetime should be represented as in ISO8601

[turicas]

The ISO8601 specification requires a T between date and time (<date>T<time>), not a space (as currently implemented by flask_peewee).

Would be nice to explicitly specify the timezone also - if it's UTC, you just need to add a Z at the end.

Following this specification, a datetime that was converted to 2012-03-13 02:49:32 now would be 2012-03-13T02:49:32Z.

You can use datetime.datetime.isoformat method to serialize it accordingly. The packages iso8601 and python-dateutil may help in deserialization, if needed.