New submission from matt farrugia <m...@far.in.net>:
The json module allows a user to provide an `object_hook` function, which, if
provided, is called to transform the dict that is created as a result of
parsing a JSON Object.
It'd be nice if there was something analogous for JSON Arrays: an `array_hook`
function to transform the list that is created as a result of parsing a JSON
Array.
At the moment transforming JSON Arrays requires one of the following approaches
(as far as I can see):
(1) Providing an object_hook function that will recursively transform any lists
in the values of an Object/dict, including any nested lists, AND recursively
transforming the final result in the event that the top level JSON object being
parsed is an array (this array is never inside a JSON Object that goes through
the `object_hook` transformation).
(2) Transforming the entire parsed result after parsing is finished by
recursively transforming any lists in the final result, including recursively
traversing nested lists AND nested dicts.
Providing an array_hook would cut out the need for either approach, as the
recursive case from the recursive functions I mentioned could be used as the
`array_hook` function directly (without the recursion).
## An example of usage:
Let's say we want JSON Arrays represented using tuples rather than lists, e.g.
so that they are hashable straight out-of-the-(json)-box. Before this
enhancement, this change requires one of the two methods I mentioned above. It
is not so difficult to implement these recursive functions, but seems
inelegant. After the change, `tuple` could be used as the `array_hook` directly:
```
>>> json.loads('{"foo": [[1, 2], "spam", [], ["eggs"]]}', array_hook=tuple)
{'foo': ((1, 2), 'spam', (), ('eggs',))}
```
It seems (in my opinion) this is more elegant than converting via an
`object_hook` or traversing the whole structure after parsing.
## The patch:
I am submitting a patch that adds an `array_hook` kwarg to the `json` module's
functions `load` and `loads`, and to the `json.decoder` module's `JSONDecoder`,
`JSONArray` and `JSONObject` classes. I also hooked these together in the
`json.scanner` module's `py_make_scanner` function.
It seems that `json.scanner` will prefer the `c_make_scanner` function defined
in `Modules/_json.c` when it is available. I am not confident enough in my C
skills or C x Python knowledge to dive into this module and make the analogous
changes. But I assume they will be simple for someone who can read C x Python
code, and that the changes will be analogous to those required to
`Lib/json/scanner.py`. I need help to accomplish this part of the patch.
## Testing:
In the mean time, I added a test to `test_json.test_decode`. It's CURRENTLY
FAILING because the implementation of the patch is incomplete (I believe this
is only due to the missing part of the patch---the required changes to
`Modules/_json.c` I identified above).
When I manually reset `json.scanner.make_scanner` to
`json.scanner.py_make_scanner` and play around with the new `array_hook`
functionality, it seems to work.
----------
components: Extension Modules, Library (Lib)
messages: 340957
nosy: matomatical
priority: normal
severity: normal
status: open
title: Add 'array_hook' for json module
type: enhancement
versions: Python 3.8
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Python tracker <rep...@bugs.python.org>
<https://bugs.python.org/issue36738>
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