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truncate() changes current stream position #76409

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andreymal mannequin opened this issue Dec 5, 2017 · 4 comments
Closed

truncate() changes current stream position #76409

andreymal mannequin opened this issue Dec 5, 2017 · 4 comments
Labels
3.7 (EOL) end of life topic-IO type-bug An unexpected behavior, bug, or error

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@andreymal
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Mannequin

andreymal mannequin commented Dec 5, 2017

BPO 32228
Nosy @pitrou, @nitishch, @andreymal
PRs
  • bpo-32228: Reset raw_pos after unwinding the raw stream #4858
  • [3.6] bpo-32228: Reset raw_pos after unwinding the raw stream (GH-4858) #5389
    		•
    Files
  • wtf1.py
    		•

    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 2018-01-28.17:44:00.391>
created_at = <Date 2017-12-05.23:19:14.742>
labels = ['type-bug', '3.7', 'expert-IO']
title = 'truncate() changes current stream position'
updated_at = <Date 2018-01-28.17:44:00.388>
user = 'https://github.com/andreymal'

    bugs.python.org fields:

    activity = <Date 2018-01-28.17:44:00.388>
actor = 'pitrou'
assignee = 'none'
closed = True
closed_date = <Date 2018-01-28.17:44:00.391>
closer = 'pitrou'
components = ['IO']
creation = <Date 2017-12-05.23:19:14.742>
creator = 'andreymal'
dependencies = []
files = ['47321']
hgrepos = []
issue_num = 32228
keywords = ['patch']
message_count = 4.0
messages = ['307698', '310962', '310973', '310974']
nosy_count = 3.0
nosy_names = ['pitrou', 'nitishch', 'andreymal']
pr_nums = ['4858', '5389']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue32228'
versions = ['Python 3.6', 'Python 3.7']
    @andreymal
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    andreymal mannequin commented Dec 5, 2017

    See attached file.

    As documentation about "truncate" says, "The current stream position isn’t changed." This is true for most cases. But this is not true for "wtf1.py" example. If you run it with Linux (Tested Debian 8 and Arch; Windows was not tested by me) and Python 3.3+ (or with Python 2.7 using backported "io" module), then these lines:

    print('tell:', fp.tell())
print('truncate:', fp.truncate())
print('tell again:', fp.tell())

    prints this:

    tell: 4098
    truncate: 4098
    tell again: 4

    As you can see, "tell" before truncate and "tell" after truncate are different. Looks like bug.

    This bug will not reproduce with Python 2.7 and builtin "open" function; it affects only "io.open".

    @andreymal andreymal mannequin added the topic-IO label Dec 5, 2017
    @andreymal andreymal mannequin changed the title truncate() changes tell() result truncate() changes current stream position Dec 5, 2017
    @andreymal andreymal mannequin added the type-bug An unexpected behavior, bug, or error label Dec 5, 2017
    @pitrou
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    pitrou commented Jan 28, 2018

    New changeset 059f58c by Antoine Pitrou (Nitish Chandra) in branch 'master':
    bpo-32228: Reset raw_pos after unwinding the raw stream (bpo-4858)
    059f58c

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    pitrou commented Jan 28, 2018

    New changeset 1d896ed by Antoine Pitrou in branch '3.6':
    [3.6] bpo-32228: Reset raw_pos after unwinding the raw stream (GH-4858) (bpo-5389)
    1d896ed

    @pitrou
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    pitrou commented Jan 28, 2018

    I've now pushed Nitish's fix to 3.7 and 3.6. I have no interest in backporting to 2.7 at this point. Closing!

    @pitrou pitrou added the 3.7 (EOL) end of life label Jan 28, 2018
    @pitrou pitrou closed this as completed Jan 28, 2018
    @ezio-melotti ezio-melotti transferred this issue from another repository Apr 10, 2022
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