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Add inspect.Signature.from_text(). #81678

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Add inspect.Signature.from_text().#81678
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ericsnowcurrently
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stdlibStandard Library Python modules in the Lib/ directorytype-featureA feature request or enhancement

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@ericsnowcurrently
ericsnowcurrently
opened on Jul 4, 2019
BPO 37497
Nosy @ericsnowcurrently, @1st1
PRs
  • gh-81678: Add inspect.Signature.from_text() #14579
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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 = 'https://github.com/ericsnowcurrently'
closed_at = None
created_at = <Date 2019-07-04.00:11:26.728>
labels = ['type-feature', 'library', '3.9']
title = 'Add inspect.Signature.from_text().'
updated_at = <Date 2020-03-06.20:46:18.865>
user = 'https://github.com/ericsnowcurrently'

    bugs.python.org fields:

    activity = <Date 2020-03-06.20:46:18.865>
actor = 'yselivanov'
assignee = 'eric.snow'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)']
creation = <Date 2019-07-04.00:11:26.728>
creator = 'eric.snow'
dependencies = []
files = []
hgrepos = []
issue_num = 37497
keywords = []
message_count = 5.0
messages = ['347250', '347251', '362765', '363535', '363551']
nosy_count = 2.0
nosy_names = ['eric.snow', 'yselivanov']
pr_nums = ['14579']
priority = 'normal'
resolution = None
stage = 'needs patch'
status = 'open'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue37497'
versions = ['Python 3.9']

    Activity

    1. ericsnowcurrently commented on Jul 4, 2019

      @ericsnowcurrently
      ericsnowcurrently
      on Jul 4, 2019
      MemberAuthor

      In early 2014 (3.3), when argument clinic was added, we added support for turning func.__text_signature__ into an inspect.Signature object. However, the functionality to convert a string into a Signature was never exposed publicly. Here's a patch to do so.

      Note that inspect.signature() will also support taking a string.

    2. ericsnowcurrently
      added
      3.9 (EOL)end of life
      on Jul 4, 2019
    3. ericsnowcurrently
      self-assigned this
      on Jul 4, 2019
    4. ericsnowcurrently
      added
      stdlibStandard Library Python modules in the Lib/ directory
      type-featureA feature request or enhancement
      on Jul 4, 2019

    5. ericsnowcurrently commented on Jul 4, 2019

      @ericsnowcurrently
      ericsnowcurrently
      on Jul 4, 2019
      MemberAuthor

      Note that there has been a little discussion of this in the past, particularly around the time that argument clinic was introduced: https://bugs.python.org/issue23967#msg241140.

    6. 1st1 commented on Feb 27, 2020

      @1st1
      1st1
      on Feb 27, 2020
      Member

      What's the actual use case for exposing this functionality?

    7. ericsnowcurrently commented on Mar 6, 2020

      @ericsnowcurrently
      ericsnowcurrently
      on Mar 6, 2020
      MemberAuthor

      Honestly, I don't recall exactly the concrete use case for which I opened this. :) I *think* it was related to applying a more restrictive signature onto an existing function (e.g. with a decorator).

    8. 1st1 commented on Mar 6, 2020

      @1st1
      1st1
      on Mar 6, 2020
      Member

      I'd be fine with Signature.from_text(), but not with Signature constructor / signature() function accepting both callable and string arguments. Overall, I think that we ought to have a real need to add this new API, so unless there's a good (or any, really) use case I'd say we shouldn't merge this now.

    9. ezio-melotti
      transferred this issue fromon Apr 10, 2022
    10. erlend-aasland
      removed
      3.9 (EOL)end of life
      on Jan 8, 2024
    11. serhiy-storchaka
      added this to Inspect issues 🔍on Mar 5, 2024

    12. tungol commented on Dec 8, 2024

      @tungol
      tungol
      on Dec 8, 2024
      Contributor

      This came up for me recently. I wanted to create a better signature for a built-in class's __init__ method by converting the signature from the underlying class. The text of the signature was easy to manipulate, but then I had no way to convert it to a signature object.

      I worked around it by creating the signature object for the underlying class first, and then modifying it with replace(). That's not a bad work-around, but there were a couple extra considerations that I thought were slightly easier to handle when generating the text of the signature I wanted directly.

      I agree that that's no need for inspect.signature() to understand the text format itself.

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