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tracemalloc.Traceback.format() should have an option to reverse the traceback #76302

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pitrou opened this issue Nov 23, 2017 · 9 comments
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tracemalloc.Traceback.format() should have an option to reverse the traceback #76302

pitrou opened this issue Nov 23, 2017 · 9 comments
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3.7 (EOL) end of life stdlib Python modules in the Lib dir type-feature A feature request or enhancement

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@pitrou
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pitrou commented Nov 23, 2017

BPO 32121
Nosy @pitrou, @vstinner, @serhiy-storchaka, @Jesse-Bakker
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  • bpo-32121: Add reverse argument to tracemalloc.Traceback.format #4534
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    GitHub fields:

    assignee = None
closed_at = <Date 2017-11-29.23:05:52.607>
created_at = <Date 2017-11-23.20:10:20.707>
labels = ['3.7', 'type-feature', 'library']
title = 'tracemalloc.Traceback.format() should have an option to reverse the traceback'
updated_at = <Date 2017-11-29.23:05:52.606>
user = 'https://github.com/pitrou'

    bugs.python.org fields:

    activity = <Date 2017-11-29.23:05:52.606>
actor = 'vstinner'
assignee = 'none'
closed = True
closed_date = <Date 2017-11-29.23:05:52.607>
closer = 'vstinner'
components = ['Library (Lib)']
creation = <Date 2017-11-23.20:10:20.707>
creator = 'pitrou'
dependencies = []
files = []
hgrepos = []
issue_num = 32121
keywords = ['patch']
message_count = 9.0
messages = ['306856', '306859', '306863', '306885', '306886', '306892', '306897', '307272', '307273']
nosy_count = 4.0
nosy_names = ['pitrou', 'vstinner', 'serhiy.storchaka', 'jbakker']
pr_nums = ['4534']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue32121'
versions = ['Python 3.7']
    @pitrou
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    pitrou commented Nov 23, 2017

    Right now tracemalloc.Traceback.format() returns the frames in "most recent call first" order. This is not intuitive since ordinary Python tracebacks are displayed in "most recent call last" order. It would be nice to add a reverse argument to change that.

    @pitrou pitrou added 3.7 (EOL) end of life stdlib Python modules in the Lib dir type-feature A feature request or enhancement labels Nov 23, 2017
    @vstinner
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    The option seems reasonable. Would you like to work on a pull request?

    @Jesse-Bakker
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    Jesse-Bakker mannequin commented Nov 24, 2017

    I can work on this if you want. Can have a PR ready in a few minutes.

    @vstinner
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    tracemalloc.Traceback contains "raw" data from the C _tracemalloc module. But since we are at Python level, we are free to change how data is rendered to user.

    Since Antoine Pitrou was surprised by the current frame order in Traceback.format() ("This is not intuitive since ordinary Python tracebacks are displayed in "most recent call last" order"), what do you think of adding a new parameter but also **reverse frames by default**?

    Maybe we can go further and even reverse frames in Traceback constructor? This is a backward incompatible change, but I don't think that a lot of code in the wild uses the tracemalloc *API*.

    About the parameter name: I'm ok with "reverse". *But* if we reverse by default, the "reverse" name can be confusing. Maybe we can use a less confusing name like "most_recent_last=True" (or "most_recent_first=False")?

    --

    Note: The faulthandler module also dumps starting with the "(most recent call first)", but I don't want to change that. It's for technical reason: faulthandler is called when something really bad happens and so Python internal structures may be corrupted. Moreover, frames is a single chained list, it's hard to iterate over them in the backward order (especially in faulthandler code where heap memory allocations are denied).

    @pitrou
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    pitrou commented Nov 24, 2017

    what do you think of adding a new parameter but also **reverse frames by default**?

    This would be fine with me. I didn't want to suggest it because it would break compatibility but obviously I find the current behaviour annoying :-)

    @serhiy-storchaka
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    While we are here, what if make a negative limit truncating from the opposite side, as in the traceback module?

    @vstinner
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    Serhiy:

    While we are here, what if make a negative limit truncating from the opposite side, as in the traceback module?

    Why not. I'm not opposed to that :-)

    @vstinner
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    New changeset 706e10b by Victor Stinner (Jesse-Bakker) in branch 'master':
    bpo-32121: Add most_recent_first parameter to tracemalloc.Traceback.format (bpo-4534)
    706e10b

    @vstinner
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    Jesse Bakker implemented all requested changes, I merged his PR. Well done, Jesse!

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