On Fri, Jan 5, 2018 at 1:45 PM, Stephan Doliov <[email protected]>
wrote:
> Hi,
> I am diving ever deeper into Django and I came upon some behavior that
> frustrated me but perhaps I am just misunderstanding what should happen and
> why.
>
> In writing unit tests for code, I wanted to write one that traps a
> json.decoder.JSONDecodeError by passing in some malformed JSON.
>
> What appears to happen however, is that Django only reports back the very
> last exception that was raised.
>
> In the case of json.decoder.JSONDecodeError, it's initialization raises a
> ValueError here is the code of json.decoder.JSONDecodeError (from my python
> 3.5 install)
>
> class JSONDecodeError(ValueError):
> """Subclass of ValueError with the following additional properties:
>
>
> msg: The unformatted error message
> doc: The JSON document being parsed
> pos: The start index of doc where parsing failed
> lineno: The line corresponding to pos
> colno: The column corresponding to pos
>
>
> """
> # Note that this exception is used from _json
> def __init__(self, msg, doc, pos):
> lineno = doc.count('\n', 0, pos) + 1
> colno = pos - doc.rfind('\n', 0, pos)
> errmsg = '%s: line %d column %d (char %d)' % (msg, lineno, colno,
> pos)
> ValueError.__init__(self, errmsg)
> self.msg = msg
> self.doc = doc
> self.pos = pos
> self.lineno = lineno
> self.colno = colno
>
>
> def __reduce__(self):
> return self.__class__, (self.msg, self.doc, self.pos)
>
>
>
> Once my django parsing code (default django rest framework 3.7.7) steps
> into here, it's own ParseError class sees only the ValueError (which
> redacts the faulty input JSON).
>
This is it, the exception is catch by DRF
>
> Is this a feature? A bug? Something in between?
>
> My desired behavior would be that i could access the JSONDecodeError
> instances doc property to go back and find out exactly which malformed JSON
> was ruining my ability to serve a complete request.
>
> Is there a way I can get Django to make visible the underlying
> JSONDecodeError (that drove a Value Error that django rest framework then
> presents to me wrapped in its ParseError class)?
>
> Clearly, I could change the underlying JSON Decoder code to my liking,
> either by changing it's errmsg or by subclassing (ValueError) it in a way
> to provide more rich information back upstream? If I run some sample code
> just in python CLI (less django) I get the whole JSONDecodeError exception
> as I desire. So I suspect modding the decoder class is not really what I
> want. But it would be nice if much like a stack trace, I could access
> ParseError instantianted by ValueError instantiated by JSONDecodeError so
> that I could access all the properties of the underlying error
> (JSONDecodeError). Should I make a feature request? Or is there already a
> toggle I can control somewhere to do this?
>
Refer to the DRF code and see if you can modify it. If you want to make a
feature request, you will have to do it in DRF
>
> Thanks,
> Steve
>
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