[issue38293] Deepcopying property objects results in unexpected TypeError

[Guðni Nathan]

New submission from Guðni Nathan :

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 "", line 1, in 
  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.

--
components: Library (Lib)
messages: 353375
nosy: Guðni Nathan
priority: normal
severity: normal
status: open
title: Deepcopying property objects results in unexpected TypeError
type: behavior
versions: Python 3.7

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[issue38293] Deepcopying property objects results in unexpected TypeError

[Guðni Nathan]

Guðni Nathan  added the comment:

A small change:

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

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[issue38293] Deepcopying property objects results in unexpected TypeError

[Guðni Nathan]

Guðni Nathan  added the comment:

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

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[issue38293] Deepcopying property objects results in unexpected TypeError

[Guðni Nathan]

Guðni Nathan  added the comment:

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 "", line 1, in 
  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

--

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[issue38293] Deepcopying property objects results in unexpected TypeError

[Guðni Nathan]

Change by Guðni Nathan :


--
keywords: +patch
pull_requests: +16016
stage:  -> patch review
pull_request: https://github.com/python/cpython/pull/16438

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