[issue31486] calling a _json.Encoder object raises a SystemError in case obj.items() returned a tuple

[Irit Katriel]

Irit Katriel  added the comment:

Closing as fixed since it's too late to change 3.6 (if that did not happen yet).

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nosy: +iritkatriel

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[issue31486] calling a _json.Encoder object raises a SystemError in case obj.items() returned a tuple

[Irit Katriel]

Change by Irit Katriel :


--
resolution:  -> fixed
stage: needs patch -> resolved
status: open -> closed
versions: +Python 3.7 -Python 3.6

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[issue31486] calling a _json.Encoder object raises a SystemError in case obj.items() returned a tuple

[Serhiy Storchaka]

Serhiy Storchaka  added the comment:

bpo-28280 fixed this issue only in the master branch. I had left this issue 
open for fixing 3.6.

--
resolution: out of date -> 
stage: resolved -> needs patch
status: closed -> open

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[issue31486] calling a _json.Encoder object raises a SystemError in case obj.items() returned a tuple

[Berker Peksag]

Berker Peksag  added the comment:

PR 3840 has been merged and it looks like Oren was correct. I'm getting the 
following output with current master:

>>> encoder(obj=BadDict({'spam': 42}), _current_indent_level=4)
['{}']

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nosy: +berker.peksag
resolution:  -> out of date
stage: needs patch -> resolved
status: open -> closed

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[issue31486] calling a _json.Encoder object raises a SystemError in case obj.items() returned a tuple

[Serhiy Storchaka]

Change by Serhiy Storchaka :


--
stage:  -> needs patch
versions: +Python 3.6 -Python 3.7

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[issue31486] calling a _json.Encoder object raises a SystemError in case obj.items() returned a tuple

[Oren Milman]

Oren Milman  added the comment:

ISTM that PR 3840 resolved this issue (as part of bpo-28280).

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[issue31486] calling a _json.Encoder object raises a SystemError in case obj.items() returned a tuple

[Serhiy Storchaka]

Serhiy Storchaka added the comment:

Oh, I was aware of this issue for long time, but didn't have good opportunity 
for fixing it. And yes, making PyMapping_Items() (and friends) always returning 
a list looks like a reasonable option to me. This could fix similar bugs in 
third-party extensions. In Python 2 PyMapping_Items() is documented as 
returning a list, but actually it can return an arbitrary type. Authors of 
extensions could be fooled by the documentation and use concrete list API.

The drawback of this solution is some performance degradation in rare case of 
items() returning a tuple.

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nosy: +rhettinger, serhiy.storchaka

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[issue31486] calling a _json.Encoder object raises a SystemError in case obj.items() returned a tuple

[Oren Milman]

New submission from Oren Milman:

the following code causes a SystemError:

import json.encoder
class BadDict(dict):
def items(self):
return ()

encoder = json.encoder.c_make_encoder(None, None, None, None, 'foo', 'bar',
  True, None, None)
encoder(obj=BadDict({'spam': 42}), _current_indent_level=4)


this is because encoder_call() (in Modules/_json.c) passes the 'obj' argument
so that eventually encoder_listencode_dict() calls PyMapping_Items() on it.
encoder_listencode_dict() assumes that PyMapping_Items() returned a list, and
passes it to PyList_Sort().


ISTM that subclassing dict and implementing items() so that it returns a tuple
is not unrealistic.

maybe we should silently convert the tuple that PyMapping_Items() returned to a
list?

--
components: Extension Modules
messages: 302278
nosy: Oren Milman
priority: normal
severity: normal
status: open
title: calling a _json.Encoder object raises a SystemError in case obj.items() 
returned a tuple
type: behavior
versions: Python 3.7

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