Ignored exceptions in test_memoryio

[pitrou]

BPO	37054
Nosy	@pitrou, @vstinner, @miss-islington
PRs	bpo-37054, _pyio: Fix BytesIO and TextIOWrapper __del__() #13601 [3.7] bpo-37054, _pyio: Fix BytesIO and TextIOWrapper __del__() (GH-13601) #13604

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = <Date 2019-05-28.00:19:06.620>
created_at = <Date 2019-05-26.14:54:40.062>
labels = ['tests', '3.8', 'type-bug', 'library']
title = 'Ignored exceptions in test_memoryio'
updated_at = <Date 2019-05-28.00:19:06.615>
user = 'https://github.com/pitrou'

bugs.python.org fields:

activity = <Date 2019-05-28.00:19:06.615>
actor = 'vstinner'
assignee = 'none'
closed = True
closed_date = <Date 2019-05-28.00:19:06.620>
closer = 'vstinner'
components = ['Library (Lib)', 'Tests']
creation = <Date 2019-05-26.14:54:40.062>
creator = 'pitrou'
dependencies = []
files = []
hgrepos = []
issue_num = 37054
keywords = ['patch']
message_count = 7.0
messages = ['343552', '343652', '343653', '343700', '343709', '343718', '343720']
nosy_count = 3.0
nosy_names = ['pitrou', 'vstinner', 'miss-islington']
pr_nums = ['13601', '13604']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue37054'
versions = ['Python 3.8']

[pitrou]

I see the following kind of exceptions when running test_memoryio:

Exception ignored in: <function IOBase.__del__ at 0x7f7cd44f49b0>
Traceback (most recent call last):
  File "/home/antoine/cpython/default/Lib/_pyio.py", line 409, in __del__
    self.close()
  File "/home/antoine/cpython/default/Lib/_pyio.py", line 2152, in close
    if self.buffer is not None and not self.closed:
  File "/home/antoine/cpython/default/Lib/_pyio.py", line 2093, in buffer
    return self._buffer
AttributeError: 'StringIO' object has no attribute '_buffer'
Exception ignored in: <function IOBase.__del__ at 0x7f7cd44f49b0>
Traceback (most recent call last):
  File "/home/antoine/cpython/default/Lib/_pyio.py", line 409, in __del__
    self.close()
  File "/home/antoine/cpython/default/Lib/_pyio.py", line 2152, in close
    if self.buffer is not None and not self.closed:
  File "/home/antoine/cpython/default/Lib/_pyio.py", line 2093, in buffer
    return self._buffer
AttributeError: 'StringIO' object has no attribute '_buffer'
ok

It seems this could be related to bpo-18748.

[vstinner]

Multiple tests log an "Exception ignored", but all of them come from the Python implementation.

The problem is that _pyio.BytesIO and _pyio.TextIOWrapper initialize their self._buffer and self._seekable attribute "later" in the constructor, but then expect these attribute to exist in __del__().

Example:

>> import _pyio; _pyio.BytesIO(b'data', foo=b'fat')

Exception ignored in: <function IOBase.__del__ at 0x7f1874c5c550>
Traceback (most recent call last):
  File "/home/vstinner/prog/python/master/Lib/_pyio.py", line 409, in __del__
    self.close()
  File "/home/vstinner/prog/python/master/Lib/_pyio.py", line 903, in close
    self._buffer.clear()
AttributeError: 'BytesIO' object has no attribute '_buffer'

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: __init__() got an unexpected keyword argument 'foo'

BytesIO.__init__() is not even called.

An easy fix would be to do nothing in __del__() if hasattr(self, '_buffer') if false.

[pitrou]

Or to add _buffer = None at the class level.

[vstinner]

Antoine:

Or to add _buffer = None at the class level.

Ok, I wrote bpo-13601 to implement this idea and fix test_memoryio warnings.

[vstinner]

New changeset a356841 by Victor Stinner in branch 'master':
bpo-37054, _pyio: Fix BytesIO and TextIOWrapper __del__() (GH-13601)
a356841

[miss-islington]

New changeset 0f352d4 by Miss Islington (bot) in branch '3.7':
bpo-37054, _pyio: Fix BytesIO and TextIOWrapper __del__() (GH-13601)
0f352d4

[vstinner]

Thanks for the report Antoine. It is now fixed in 3.7 and master branches.