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Deepcopying property objects results in unexpected TypeError #82474

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GudniNatan mannequin opened this issue Sep 27, 2019 · 9 comments
Closed

Deepcopying property objects results in unexpected TypeError #82474

GudniNatan mannequin opened this issue Sep 27, 2019 · 9 comments
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3.7 (EOL) end of life 3.8 only security fixes 3.9 only security fixes stdlib Python modules in the Lib dir type-bug An unexpected behavior, bug, or error

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@GudniNatan
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GudniNatan mannequin commented Sep 27, 2019

BPO 38293
Nosy @serhiy-storchaka, @eamanu, @miss-islington, @GudniNatan
PRs
  • bpo-38293: Allow shallow and deep copying of property objects #16438
  • [3.7] bpo-38293: Allow shallow and deep copying of property objects (GH-16438) #17968
  • [3.8] bpo-38293: Allow shallow and deep copying of property objects (GH-16438) #17969
    		•

    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 2020-01-12.17:43:50.420>
created_at = <Date 2019-09-27.16:16:43.481>
labels = ['3.7', '3.8', 'type-bug', 'library', '3.9']
title = 'Deepcopying property objects results in unexpected TypeError'
updated_at = <Date 2020-01-12.18:04:21.916>
user = 'https://github.com/GudniNatan'

    bugs.python.org fields:

    activity = <Date 2020-01-12.18:04:21.916>
actor = 'miss-islington'
assignee = 'none'
closed = True
closed_date = <Date 2020-01-12.17:43:50.420>
closer = 'cheryl.sabella'
components = ['Library (Lib)']
creation = <Date 2019-09-27.16:16:43.481>
creator = 'GudniNatan'
dependencies = []
files = []
hgrepos = []
issue_num = 38293
keywords = ['patch']
message_count = 9.0
messages = ['353375', '353376', '353377', '353383', '353388', '353428', '359857', '359860', '359861']
nosy_count = 4.0
nosy_names = ['serhiy.storchaka', 'eamanu', 'miss-islington', 'GudniNatan']
pr_nums = ['16438', '17968', '17969']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue38293'
versions = ['Python 3.7', 'Python 3.8', 'Python 3.9']
    @GudniNatan
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    GudniNatan mannequin commented Sep 27, 2019

    Currently, attempting to deepcopy a property object will result in an unexpected TypeError:

    >>> import copy
>>> obj = property()
>>> new_obj = copy.deepcopy(obj)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "C:\Program Files\WindowsApps\PythonSoftwareFoundation.Python.3.7_3.7.1264.0_x64__qbz5n2kfra8p0\lib\copy.py", line 169, in deepcopy
    rv = reductor(4)
TypeError: can't pickle property objects

    What I believe is happening here is that since property objects are not treated by the copy module as atomic, they are passed off to be pickled and so our error is raised.
    This can be fixed in a similar manner to how it works for type objects, function objects and more.
    Adding a single line of code to Lib/copy.py after line 208:

    d[property] = _deepcopy_atomic

    Means that property objects will be treated as atomic, and therefore returned as-is.

    @GudniNatan GudniNatan mannequin added 3.7 (EOL) end of life stdlib Python modules in the Lib dir type-bug An unexpected behavior, bug, or error labels Sep 27, 2019
    @GudniNatan
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    GudniNatan mannequin commented Sep 27, 2019

    A small change:

    The fix should go to Lib/copy.py:198, not line 208.

    @serhiy-storchaka
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    But the property object is not atomic. It's attribute __doc__ is writeable.

    @GudniNatan
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    GudniNatan mannequin commented Sep 27, 2019

    Function objects are considered "atomic" here and I believe you can also write to their __doc__ (among other attributes).

    @GudniNatan
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    GudniNatan mannequin commented Sep 27, 2019

    This bug appears to also affect shallow copies and can be reproduced with the following code:

    >>> import copy
>>> obj = property()
>>> copy.copy(obj)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "C:\Program Files\WindowsApps\PythonSoftwareFoundation.Python.3.7_3.7.1264.0_x64__qbz5n2kfra8p0\lib\copy.py", line 96, in copy
    rv = reductor(4)
TypeError: can't pickle property objects

    @eamanu
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    eamanu mannequin commented Sep 27, 2019

    I can confirm this behavior also on python 3.6 3.8 3.9

    @eamanu eamanu mannequin added 3.8 only security fixes 3.9 only security fixes labels Sep 27, 2019
    @miss-islington
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    New changeset 9f3fc6c by Miss Islington (bot) (Guðni Natan Gunnarsson) in branch 'master':
    bpo-38293: Allow shallow and deep copying of property objects (GH-16438)
    9f3fc6c

    @miss-islington
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    New changeset 4be9726 by Miss Islington (bot) in branch '3.7':
    bpo-38293: Allow shallow and deep copying of property objects (GH-16438)
    4be9726

    @miss-islington
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    New changeset 3043ec7 by Miss Islington (bot) in branch '3.8':
    bpo-38293: Allow shallow and deep copying of property objects (GH-16438)
    3043ec7

    @ezio-melotti ezio-melotti transferred this issue from another repository Apr 10, 2022
    @stuaxo stuaxo mentioned this issue Jul 21, 2022
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