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io.BufferedReader.writabe is False, but io.BufferedReader.truncate does not raise OSError #80131

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steverpalmer mannequin opened this issue Feb 9, 2019 · 2 comments
Closed

io.BufferedReader.writabe is False, but io.BufferedReader.truncate does not raise OSError #80131

steverpalmer mannequin opened this issue Feb 9, 2019 · 2 comments
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3.9 only security fixes topic-IO

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@steverpalmer
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Mannequin

steverpalmer mannequin commented Feb 9, 2019

BPO 35950
Nosy @berkerpeksag, @vadmium, @miss-islington, @steverpalmer
PRs
  • bpo-35950: Raise OSError in io.BufferedReader.truncate() #13689
  • bpo-35950: Raise UnsupportedOperation in BufferedReader.truncate() #18586
    		•

    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 2020-02-21.18:01:25.803>
created_at = <Date 2019-02-09.13:36:22.181>
labels = ['3.9', 'expert-IO']
title = 'io.BufferedReader.writabe is False, but io.BufferedReader.truncate does not raise OSError'
updated_at = <Date 2020-02-22.07:19:05.846>
user = 'https://github.com/steverpalmer'

    bugs.python.org fields:

    activity = <Date 2020-02-22.07:19:05.846>
actor = 'berker.peksag'
assignee = 'none'
closed = True
closed_date = <Date 2020-02-21.18:01:25.803>
closer = 'methane'
components = ['IO']
creation = <Date 2019-02-09.13:36:22.181>
creator = 'steverpalmer'
dependencies = []
files = []
hgrepos = []
issue_num = 35950
keywords = ['patch']
message_count = 2.0
messages = ['335132', '362417']
nosy_count = 4.0
nosy_names = ['berker.peksag', 'martin.panter', 'miss-islington', 'steverpalmer']
pr_nums = ['13689', '18586']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue35950'
versions = ['Python 3.9']
    @steverpalmer
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    steverpalmer mannequin commented Feb 9, 2019

    An io.BUfferedReader object has an (inherited) writable method that returns False. io.IOBase states in the description of the writable method that "If False, write() and truncate() will raise OSError."

    However, if the BufferedReader object is constructed from a writabe io.RawIOBase object, then the truncate does not raise the exception.

    >>> import io
>>> import tempfile
>>> rf = tempfile.TemporaryFile(buffering=0)
>>> rf
<_io.FileIO name=3 mode='rb+' closefd=True>
>>> bf = io.BufferedReader(rf)
>>> bf.writable()
False
>>> bf.truncate(0)
0

    Looking at _pyio.py file, the truncate method in the _BufferedIOMixin wrapper class delegates the truncation to it's raw attribute. If the raw element permits the truncation, then it will proceed regardless of the writable state of the wrapper class. I'd suggest that modifying the truncate method in _BufferedIOMixin to raise OSError (or Unsupported) if not self.writable() could fix this problem.

    @steverpalmer steverpalmer mannequin added 3.7 (EOL) end of life topic-IO labels Feb 9, 2019
    @miss-islington
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    New changeset fd5116c by Berker Peksag in branch 'master':
    bpo-35950: Raise UnsupportedOperation in BufferedReader.truncate() (GH-18586)
    fd5116c

    @methane methane added 3.9 only security fixes and removed 3.7 (EOL) end of life labels Feb 21, 2020
    @methane methane closed this as completed Feb 21, 2020
    @ezio-melotti ezio-melotti transferred this issue from another repository Apr 10, 2022
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