I don't see why the need for standardisation exists. Here's another example because I can explain myself best by giving examples:
I have an API. I can write some classes that correspond to JSON inputs my API expects and define __json__ in them to convey how they are expected to be serialised. For example, a Person class with first_name and last_name fields being serialised as a dict with the fields in camel case instead. (Sure, normally I'd write a serialisation function as well as part of my package in this case but I'm just coming up with examples on the spot). For non standard things like date and time, many implementations of JSON already added support for it using a format I can't recall at the moment. And even if a class defines __json__ in a particular format but you would need another one, the method of making a custom JSONEncoder still remains, as __json__ functions would be attempted only after the custom default implementation. Therefore, __json__ would enable sensible defaults to be chosen while not harming the possibility of using a custom format if it is so desired. --- Dan Cojocaru On 6 Apr 2020, 22:08 +0300, Chris Angelico <ros...@gmail.com>, wrote: > On Tue, Apr 7, 2020 at 4:48 AM Andrew Barnert via Python-ideas > <python-ideas@python.org> wrote: > > That’s not true for JSON; the entire point of it is data interchange. You > > expect to be able to dump an object, send it over the wire or store it to a > > file, load it (or even parse it in JS or ObjC or Go or whatever) and get > > back an equivalent object. It’s easy to come up with ways to build on top > > of JSON to interchange things like time points or raw binary strings or > > higher-level structured objects, but they require doing something on both > > the encode side and the decode side. Just being able to encode them to > > something human-readable is useless—if I encode a datetime object, I need > > to get back a datetime (or Date or NSDate or whatever) on the other end, > > not a str (or string or NSString or whatever) that a human could tell is > > probably meant to be a datetime but will raise an exception when I try to > > subtract it from now(). > > > > (Of course JSON isn’t perfect, as anyone who’s tried to interchange, say, > > int64 values discovers… but it’s good enough for many applications.) > > > > The trouble with using JSON to interchange things that aren't in the > JSON spec is that you then have to build another layer on top of it - > a non-standard layer. That means that whatever you do, it's inherently > app-specific. For instance, I might choose to encode a datetime as a > string in ISO format, but how is the other end going to know that it > was meant to be a date? (Usually, if I'm sending something to some > front-end JavaScript, I'll just hard-code the JS to know that > thing[0].created is a timestamp, and should be parsed accordingly.) > > So if it's app-specific, then the best way to handle it is in your > app, not in the data type you're encoding. Subclassing JSONEncoder > works for this; adding a __json__ method doesn't really, unless there > is some single canonical encoding for a particular object. > > The two become close to equivalent when you're only asking about your > own custom classes. You can, in fact, create your own private __json__ > protocol (although, since it's private to you, it'd probably be better > to call the method "to_json" rather than "__json__"), and have a > subclass of JSONEncoder that calls it. It'd work fine because you > don't NEED to interoperate with other libraries. It's only when you > try to standardize something that's inherently nonstandard that things > get problematic :) > > ChrisA > _______________________________________________ > Python-ideas mailing list -- python-ideas@python.org > To unsubscribe send an email to python-ideas-le...@python.org > https://mail.python.org/mailman3/lists/python-ideas.python.org/ > Message archived at > https://mail.python.org/archives/list/python-ideas@python.org/message/4ZEQKTQ5CMZUXC6E6JVFHQS3VGYEDJ7C/ > Code of Conduct: http://python.org/psf/codeofconduct/
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