repr() on detached stream objects fails

[vadmium]

BPO	23093
Nosy	@pitrou, @benjaminp, @hynek, @vadmium, @serhiy-storchaka
Files	detach-indep.patch detach-indep.v2.patch

^{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 2014-12-22.03:01:25.375>
created_at = <Date 2014-12-20.14:19:49.437>
labels = ['type-bug', 'expert-IO']
title = 'repr() on detached stream objects fails'
updated_at = <Date 2014-12-22.03:01:25.272>
user = 'https://github.com/vadmium'

bugs.python.org fields:

activity = <Date 2014-12-22.03:01:25.272>
actor = 'python-dev'
assignee = 'none'
closed = True
closed_date = <Date 2014-12-22.03:01:25.375>
closer = 'python-dev'
components = ['IO']
creation = <Date 2014-12-20.14:19:49.437>
creator = 'martin.panter'
dependencies = []
files = ['37516', '37523']
hgrepos = []
issue_num = 23093
keywords = ['patch']
message_count = 6.0
messages = ['232971', '232973', '232983', '232997', '232998', '233006']
nosy_count = 7.0
nosy_names = ['pitrou', 'benjamin.peterson', 'stutzbach', 'python-dev', 'hynek', 'martin.panter', 'serhiy.storchaka']
pr_nums = []
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue23093'
versions = ['Python 2.7', 'Python 3.4', 'Python 3.5']

[vadmium]

Patch to fix the underlying issue I mentioned in msg230955. After calling detach() on one of the BufferedIOBase wrappers or a TextIOWrapper, most operations will raise an exception. My patch ensures the following operations are still usable, because they are documented and it doesn’t make sense to disable them:

repr(stream)
stream.encoding
stream.errors
stream.line_buffering

[serhiy-storchaka]

The issue is still here.

>>> f = open('/dev/null')
>>> f
<_io.TextIOWrapper name='/dev/null' mode='r' encoding='UTF-8'>
>>> f.buffer.detach()
<_io.FileIO name='/dev/null' mode='rb' closefd=True>
>>> f
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: raw stream has been detached

Python implementation works.

>>> import _pyio
>>> f = _pyio.open('/dev/null')
>>> f
<_pyio.TextIOWrapper name='/dev/null' mode='r' encoding='UTF-8'>
>>> f.buffer.detach()
<_io.FileIO name='/dev/null' mode='rb' closefd=True>
>>> f
<_pyio.TextIOWrapper mode='r' encoding='UTF-8'>
>>> f = _pyio.open('/dev/null')
>>> f.detach()
<_pyio.BufferedReader name='/dev/null'>
>>> f
<_pyio.TextIOWrapper mode='r' encoding='UTF-8'>
>>> f = _pyio.open('/dev/null', 'rb')
>>> f
<_pyio.BufferedReader name='/dev/null'>
>>> f.detach()
<_io.FileIO name='/dev/null' mode='rb' closefd=True>
>>> f
<_pyio.BufferedReader>

I would be good to make Python and C implementation match.

[vadmium]

Damn, detaching the intermediate buffered stream is a bit more awkward. The difference between the “io” and “_pyio” implementations boils down to:

• io.BufferedReader/Writer/RWPair.name properties raise a ValueError if the stream is detached
• _pyio._BufferedIOMixin.name property returns “self.raw.name”. When detached, “self.raw” is None, so this causes an AttributeError.

This is significant because io.TextIOWrapper.__repr__() only handles AttributeError when accessing “self.buffer.name”. The best option that I can think of to fix this is to make all the repr() implementations handle this ValueError exception.

[vadmium]

Here is patch v2, which ignores any exception derived from the Exception base class when reading the self.name etc properties. I’m interested what people think of this approach.

[serhiy-storchaka]

It looks reasonable to me.

[python-dev]

New changeset f3ff3e424b6f by Benjamin Peterson in branch '3.4':
allow more operations to work on detached streams (closes bpo-23093)
https://hg.python.org/cpython/rev/f3ff3e424b6f

New changeset afa8d8ab0937 by Benjamin Peterson in branch '2.7':
allow more operations to work on detached streams (closes bpo-23093)
https://hg.python.org/cpython/rev/afa8d8ab0937

New changeset f2cfa8a348dd by Benjamin Peterson in branch 'default':
merge 3.4 (bpo-23093)
https://hg.python.org/cpython/rev/f2cfa8a348dd