| msg255131 - (view) |
Author: Serhiy Storchaka (serhiy.storchaka) *  |
Date: 2015-11-23 06:58 |
| tp_setattro and tp_setattr fields of PyTypeObject are used for deleting attributes. In this case the third argument is NULL. This should be documented. Not awareness of this can cause a segmentation fail (for example see ). |
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| msg255237 - (view) |
Author: Martin Panter (martin.panter) * |
Date: 2015-11-23 23:06 |
| Here is a patch. The same problem happens with getset descriptors: >>> del sys.stdout._CHUNK_SIZE SystemError: null argument to internal routine So I also changed the documentation for “setter” descriptor functions and the tp_descr_set() method. I only looked at the Python 3 implementation, and I understand Python 2 objects work differently in some cases, so I’m not sure if my changes are apropriate for Python 2. |
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| msg255284 - (view) |
Author: Serhiy Storchaka (serhiy.storchaka) * |
Date: 2015-11-24 18:55 |
| Thank you Martin. In general the patch LGTM, but I'm not expert in English writing. There are other functions and slots with twofold purpose: PyObject_SetItem, PySequence_SetItem, PySequence_SetSlice, PyMapping_SetItemString, PySequenceMethods.sq_ass_item, PyMappingMethods.mp_ass_subscript. May be address them in this issue? I'm not sure about documenting the deletion for PyObject_SetAttr and like. All these functions have Del-counterpart. Deleting by Set-function with NULL may be a side effect and be deprecated in future. May be worth to discuss this on Python-Dev. For PySys_SetObject the deletion if value is NULL already is documented, but there is no PySys_DelObject. |
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| msg255291 - (view) |
Author: Martin Panter (martin.panter) * |
Date: 2015-11-24 21:04 |
| I agree it might be safer not to document that PyObject_SetAttr etc can delete (move that change to the tp_setattro etc method slot). I’ll also review the other functions you mentioned when I get a chance. |
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| msg255335 - (view) |
Author: Serhiy Storchaka (serhiy.storchaka) * |
Date: 2015-11-25 11:14 |
| Python-Dev discussion: http://comments.gmane.org/gmane.comp.python.devel/155474 |
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| msg255609 - (view) |
Author: Martin Panter (martin.panter) * |
Date: 2015-11-30 05:43 |
| In the python-dev thread, Nick Coghlan gave some arguments and examples where PyObject_SetAttr() is intended to be used for deletion. So I will keep my changes for PyObject_SetAttr(), and also _SetAttrString() for consistency. My second patch documents deletion with sq_ass_item(), mp_ass_subscript(), and PySequence_SetItem(). PyObject_SetItem() does not look like it deletes items. It explicitly considers value == NULL to be an error. As a consequence, PyMapping_SetItemString() does not delete either. PySequence_SetItem() does accept NULL to delete the item. I think this is reasonable, to keep it consistent with sq_ass_item(), so I documented it. PySequence_SetSlice() also accepts NULL to delete the slice. But I am more reluctant to document this, because I don’t know of any slot or other code that would benefit. So I have left it as is for the time being. |
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| msg256014 - (view) |
Author: Serhiy Storchaka (serhiy.storchaka) * |
Date: 2015-12-06 15:30 |
| I think the conclusion of Python_Dev discussion is that it is not worth to deprecate this behavior in the code. Current behavior of PyObject_SetAttr and PySequence_SetItem should be documented with a deprecation notice. |
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| msg256034 - (view) |
Author: Martin Panter (martin.panter) * |
Date: 2015-12-06 21:51 |
| Okay, I will look at making it say deleting via SetAttr etc is possible but is not the main purpose, and using DelAttr etc is recommended instead. |
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| msg256040 - (view) |
Author: Martin Panter (martin.panter) * |
Date: 2015-12-07 01:14 |
| setattr.3.patch changes to documenting setting as the main purpose, but mentions deleting also works but is deprecated in favour of the main deletion functions. I also clarified that the slots have to support deleting via NULL. |
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| msg256056 - (view) |
Author: Serhiy Storchaka (serhiy.storchaka) * |
Date: 2015-12-07 10:02 |
| The patch LGTM. Thanks Martin. |
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| msg256096 - (view) |
Author: Roundup Robot (python-dev)  |
Date: 2015-12-08 00:07 |
| New changeset 50711c80ff76 by Martin Panter in branch '3.5': Issue #25701: Document C API functions that both set and delete objects https://hg.python.org/cpython/rev/50711c80ff76 New changeset 7bb7173cd97a by Martin Panter in branch 'default': Issue #25701: Merge set and delete documentation from 3.5 https://hg.python.org/cpython/rev/7bb7173cd97a |
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| msg256098 - (view) |
Author: Martin Panter (martin.panter) * |
Date: 2015-12-08 00:12 |
| I committed my patch to 3.5+. I will leave this open in case someone wants to look into how things work in 2.7. I presume things might be different in Python 2; all I know is there are two kinds of classes and objects, and the slots are a bit different (__setslice__?). |
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| msg256762 - (view) |
Author: Serhiy Storchaka (serhiy.storchaka) * |
Date: 2015-12-20 11:30 |
| In 2.7 all is the same except that there is the sq_ass_slice slot and the PySequence_SetSlice() function. |
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| msg281595 - (view) |
Author: Martin Panter (martin.panter) * |
Date: 2016-11-24 01:06 |
| The 2.7 patch looks okay to me. I confirmed that sq_ass_slice gets called to delete slices, and I presume the other stuff is similar to Python 3. Do you want to commit this to 2.7 Serhiy? |
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| msg281607 - (view) |
Author: Serhiy Storchaka (serhiy.storchaka) * |
Date: 2016-11-24 05:58 |
| Please do this yourself. This is mainly your patch. |
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| msg282076 - (view) |
Author: Roundup Robot (python-dev) |
Date: 2016-11-30 11:06 |
| New changeset 83e3c863594c by Martin Panter in branch '2.7': Issue #25701: Document that some C APIs can both set and delete items https://hg.python.org/cpython/rev/83e3c863594c |
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| msg282077 - (view) |
Author: Martin Panter (martin.panter) * |
Date: 2016-11-30 11:11 |
| I made one minor change: element → slice |
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