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[2.7] Add PYTHONSHOWREFCOUNT environment variable to Python 2.7 #75914

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vstinner opened this issue Oct 9, 2017 · 5 comments
Closed

[2.7] Add PYTHONSHOWREFCOUNT environment variable to Python 2.7 #75914

vstinner opened this issue Oct 9, 2017 · 5 comments

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@vstinner
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vstinner commented Oct 9, 2017

BPO 31733
Nosy @vstinner, @benjaminp, @ezio-melotti, @serhiy-storchaka, @stratakis
PRs
  • [2.7] bpo-31733: Add PYTHONSHOWREFCOUNT env var #3932
  • [2.7] bpo-31733, bpo-31692: Document 2 new env vars in What's New in Python 2.7 #4019
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    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 2017-10-17.10:03:43.361>
created_at = <Date 2017-10-09.13:44:19.479>
labels = []
title = '[2.7] Add PYTHONSHOWREFCOUNT environment variable to Python 2.7'
updated_at = <Date 2017-10-17.20:13:15.247>
user = 'https://github.com/vstinner'

    bugs.python.org fields:

    activity = <Date 2017-10-17.20:13:15.247>
actor = 'vstinner'
assignee = 'none'
closed = True
closed_date = <Date 2017-10-17.10:03:43.361>
closer = 'vstinner'
components = []
creation = <Date 2017-10-09.13:44:19.479>
creator = 'vstinner'
dependencies = []
files = []
hgrepos = []
issue_num = 31733
keywords = ['patch']
message_count = 5.0
messages = ['303952', '303962', '304491', '304496', '304526']
nosy_count = 5.0
nosy_names = ['vstinner', 'benjamin.peterson', 'ezio.melotti', 'serhiy.storchaka', 'cstratak']
pr_nums = ['3932', '4019']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue31733'
versions = ['Python 2.7']
    @vstinner
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    vstinner commented Oct 9, 2017

    When Python 2.7 is built in debug mode, it displays the total number of references when the program finishes or after each statement in the interactive interpreter.

    Example:

    haypo@selma$ ./python
Python 2.7.14+ (heads/2.7:cc4b6f1c62, Oct  9 2017, 15:30:11) 
[GCC 7.2.1 20170915 (Red Hat 7.2.1-2)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> 1+1
2
[45025 refs]
>>> 2+2
4
[45025 refs]
>>> 
[45025 refs]
[21655 refs]

    While I'm Python core developer working on reference leaks for years, I *never* used this value. I only use "python -m test -R 3:3 test_xxx" to track reference leaks.

    I really liked Python 3.4 which made this option an opt-in, python3 -X showrefcount: bpo-17323 (commit 1f8898a).

    I propose to change Python 2.7 behaviour to not print this value by default, but add a new PYTHONSHOWREFCOUNT environment variable to display it. The value is displayed if PYTHONSHOWREFCOUNT is set. Other similar existing variables:

    • PYTHONTHREADDEBUG
    • PYTHONDUMPREFS
    • PYTHONMALLOCSTATS

    https://docs.python.org/2.7/using/cmdline.html#debug-mode-variables

    I prefer to add a new environment style rather than adding a new -X command line option. IMHO an environment variable is less intrusive. For example, older Python 2.7 versions completely ignore unknown environment variables, whereas "python2.7 -X showrefcount ..." currently logs the "-X is reserved for implementation-specific arguments" message into stderr.

    Attached PR adds PYTHONSHOWREFCOUNT.

    @vstinner
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    vstinner commented Oct 9, 2017

    Since this issue is on the thin border between "feature" and "bug fix", I would like to get the feedback of Benjamin on this change.

    @benjamin: Are you ok to make such change late in the Python 2.7 cycle, in Python 2.7.15?

    @vstinner
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    New changeset 3c082a7 by Victor Stinner in branch '2.7':
    bpo-31733: Add PYTHONSHOWREFCOUNT env var (GH-3932)
    3c082a7

    @vstinner
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    Python 2.7.15 now requires to set PYTHONSHOWREFCOUNT env var to dump "[xxx refs]".

    @vstinner
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    New changeset 355393e by Victor Stinner in branch '2.7':
    [2.7] bpo-31733, bpo-31692: Document 2 new env vars in What's New in Python 2.7 (GH-4019)
    355393e

    @ezio-melotti ezio-melotti transferred this issue from another repository Apr 10, 2022
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