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).
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?
Thanks,
Steve
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