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Enhance frame handing in warnings.warn() to skip by module rather that stacklevel #39615

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Enhance frame handing in warnings.warn() to skip by module rather that stacklevel#39615
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gpshead
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stdlibStandard Library Python modules in the Lib/ directorytype-featureA feature request or enhancement

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@doerwalter
doerwalter
opened on Nov 27, 2003
BPO 850482
Nosy @doerwalter, @devdanzin, @jayvdb
Files
  • diff.txt
  • diff2.txt
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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 = None
created_at = <Date 2003-11-27.23:12:08.000>
labels = ['type-feature', 'library']
title = 'Enhance frame handing in warnings.warn()'
updated_at = <Date 2015-12-10.08:16:31.826>
user = 'https://github.com/doerwalter'

    bugs.python.org fields:

    activity = <Date 2015-12-10.08:16:31.826>
actor = 'jayvdb'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)']
creation = <Date 2003-11-27.23:12:08.000>
creator = 'doerwalter'
dependencies = []
files = ['5709', '5710']
hgrepos = []
issue_num = 850482
keywords = ['patch']
message_count = 6.0
messages = ['44953', '44954', '44955', '44956', '82016', '256170']
nosy_count = 4.0
nosy_names = ['doerwalter', 'zseil', 'ajaksu2', 'jayvdb']
pr_nums = []
priority = 'normal'
resolution = None
stage = 'patch review'
status = 'open'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue850482'
versions = ['Python 3.2']

    Linked PRs

    Activity

    1. doerwalter commented on Nov 27, 2003

      @doerwalter
      doerwalter
      on Nov 27, 2003
      ContributorAuthor

      This patch enhances warnings.warn() in the following
      way: The stacklevel passed in may be negative. In that
      case the call stack is searched for the innermost frame
      whose module name differs in the first -stacklevel
      components. This frame will be used in the report.

      So when you have the following call stack:
      m1.f()
      m1.m11.f()
      m1.m12.f()
      m2.m21.f()
      m2.m22.f()

      and the innermost function() m2.m22.f() call
      warnings.warn() with a stacklevel of -2 the frame
      reported will be from m1.m12.f(), because it is the
      first one from outside the m2 package.

    2. doerwalter
      added
      stdlibStandard Library Python modules in the Lib/ directory
      on Nov 27, 2003

    3. zseil commented on Apr 2, 2007

      @zseil
      zseilmannequin
      on Apr 2, 2007
      Mannequin

      I don't know how desireable this feature is, but
      I think that a better solution would be to add
      a new parameter to warnings.warn(), instead of
      reusing the old one.

      Also, your description is wrong; when warn() in
      your example is called with stacklevel -2, the
      reported frame is m2.m21.f(). To get your result,
      you have to call warn() with stacklevel -1.

      I think that a better solution would be to add
      a skipmodules='moduleprefix' parameter to the
      warn() function. warn() would then simply look
      for the first frame whose module name doesn't
      start with this prefix.

    4. doerwalter commented on Apr 8, 2007

      @doerwalter
      doerwalter
      on Apr 8, 2007
      ContributorAuthor

      Here's an updated patch that implements your suggestion: skipmodules is a regular expression. Any module whose name matches the RE will be skipped when determining the stacklevel.
      File Added: diff2.txt

    5. zseil commented on Apr 15, 2007

      @zseil
      zseilmannequin
      on Apr 15, 2007
      Mannequin

      Looks good to me. I like that skipmodules is a
      regular expression, but I don't know how will it
      affect the intended rewrite in C:

      http://www.python.org/sf/1631171

      It would be nice if the documentation mentioned
      what is the interaction between stacklevel and
      skipmodules parameters, at least something like:

      "If you want to issue a warning outside your module,
      and you don't know how many frames will have to be
      skipped for that, pass some big integer for stacklevel"

      If this patch is accepted, it should be put to use in
      the _struct module:

      >>> struct.Struct("<l").pack(4023029188) # note: module is sys
sys:1: DeprecationWarning: struct integer overflow masking is deprecated

    6. devdanzin commented on Feb 14, 2009

      @devdanzin
      devdanzinmannequin
      on Feb 14, 2009
      Mannequin

      Patch has tests, needs updating.

    7. devdanzin
      added
      type-featureA feature request or enhancement
      on Feb 14, 2009

    8. jayvdb commented on Dec 10, 2015

      @jayvdb
      jayvdbmannequin
      on Dec 10, 2015
      Mannequin

      See similar http://bugs.python.org/issue25216 aka #69403

    9. ezio-melotti
      transferred this issue fromon Apr 9, 2022
    10. gpshead
      changed the title [-]Enhance frame handing in warnings.warn()[/-] [+]Enhance frame handing in warnings.warn() to skip by module rather that stacklevel[/+] on Jan 1, 2023
    11. gpshead
      self-assigned this
      on Jan 1, 2023

    12. gpshead commented on Jan 1, 2023

      @gpshead
      gpshead
      on Jan 1, 2023
      Member

      Assigning to me to see if I get to this as I'm really wanting this feature while trying to add a warning deep within an an complicated package with multiple public API surfaces at different stacklevels.

    13. gpshead
      added a commit that references this issue on Jan 8, 2023

      pythongh-39615: Add warn() skip_file_prefixes= support.

      c0c19a4

    14. merwok commented on Jan 8, 2023

      @merwok
      merwok
      on Jan 8, 2023
      Member

      Skipping by module seems good, but the implementation relies on file names — could it be module or package name?

    15. gpshead commented on Jan 8, 2023

      @gpshead
      gpshead
      on Jan 8, 2023
      Member

      It seems like "by fully qualified module name" is what code authors might want as that's how we think... But in practice that might be hard to implement in a reliable manner. The __file__ module or package prefix match effectively lets you do that. Anticipated common use path prefix matching use cases: skip_file_prefixes=(__file__,) or skip_file_prefixes=(os.path.dirname(__file__),)

      Investigating... The code objects in the frame appears to have a .co_qualname attribute, but it that always set?
      Code objects are always defined within a file thus co_filename should be set for anything coming from a .py source file in a module or package (C extensions or manual code object creation could supply whatever "filename" they want, but those unusual things aren't cases I'd worry about matching and skipping), but code objects are not required to have names or qualified names (lambdas, comprehension expressions, nested functions, etc)...

      It might be possible to get the base module name itself via frame.f_globals['__name__'] but even that sounds unreliable, and using just the __name__ as a match to skip is pretty non-specific.

      I'll poke around, but I'm not sure if it is possible.

      The other constraint I've been keeping in this code: It must be a fast check. warn() should not do a lot of computation.

    16. gpshead commented on Jan 12, 2023

      @gpshead
      gpshead
      on Jan 12, 2023
      Member

      I don't believe module or package name is possible. Indeed frame.f_code.co_qualname doesn't give a module or package name. Frames and code objects don't have any reference back to a module or namespace. So I don't see any easy, fast, and reliable way to do that beyond the filename based match as my PR implements.

    17. gpshead
      added a commit that references this issue on Jan 28, 2023

      gh-39615: Add warnings.warn() skip_file_prefixes support (#100840)

      052f53d
    18. iritkatriel
      added a commit that references this issue on Jan 29, 2023

      pythongh-39615: fix warning on return type mismatch

      6f13f4c
    19. gpshead
      added a commit that references this issue on Jan 30, 2023

      gh-39615: fix warning on return type mismatch (#101407)

      c4170c3
    20. mdboom
      added 2 commits that reference this issue on Jan 31, 2023

      pythongh-39615: Add warnings.warn() skip_file_prefixes support (pytho…

      1939cb0

      pythongh-39615: fix warning on return type mismatch (python#101407)

      9f308a4

    21. gpshead commented on Feb 8, 2023

      @gpshead
      gpshead
      on Feb 8, 2023
      Member

      I'm calling this fixed as it can skip by filename now which was a performant way to implement this.

    22. gpshead
      closed this as completedon Feb 8, 2023
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