Modern Python Standard Library Cookbook

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You probably noticed that while encoding Python to JSON is fairly reasonable and robust, the trip back is full of issues.

JSON is not a very expressive language; it doesn't provide any machinery for custom types, so you have a standard way to give back hints to the decoder about the type that you would expect something to be decoded to.

While we can guess that something like 2017-01-01T13:21:17 is a date, we have no guarantee at all. Maybe, originally, it was actually some text that by chance contained something that can be decoded as a date, but was never meant to become a datetime object in Python.

For this reason, it's usually safe to implement custom decoding only in constrained environments. If you know and control the ...