[issue41871] Add PyList_Remove() in listobject.c

[STINNER Victor]

STINNER Victor  added the comment:

> it is more convenient to just call the method

Calling a Python method in Python is not convenient nor efficient.

For example, PyObject_CallMethod() has to decode a name from UTF-8 and then 
needs a lookup into the type dictionary. The list.remove() raises a exception 
if the item is not found, whereas PyCodec_Unregister() does nothing if the 
codec search function is not found: the exception is ignored.

It's also about correctness, looking for an item in a list can be tricky if the 
list size changes during the lookup, or Python can crash if it uses a borrowed 
reference whereas a list item is destroyed. There were tons of such bugs in the 
dict implementation. list.remove() doesn't look safe, but I would prefer to 
avoid having to fix the same bugs in copies of similar functions.

If a public function is not justified, what about an internal function?

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[issue41871] Add PyList_Remove() in listobject.c

[Serhiy Storchaka]

Serhiy Storchaka  added the comment:

PyList_SetSlice() allows to remove an item by index, as in `del a[i]`. 
list.remove() searches the item by value and removes the first occurrence. You 
can implement it via PySequence_Index() and PyList_SetSlice(), but it is more 
convenient to just call the method.

There is no C API for most methods of builtin types. C API is only added for 
the following cases:

1. Conversion between Python and C values. There is no other way to do this. 
PyLong_AsLong() and PyLong_FromLong().
2. Access to general protocols. PyNumber_Add(), PyObject_GetAttr(), 
PySequence_etc.
3. Specialized versions for concrete types if they are much more convenient and 
performant. They are also often preceded the more general API. 
PyObject_GetItem() -> PySequence_GetItem() -> PyList_GetItem() -> 
PyList_GET_ITEM().
4. High-level common operations. From PyImport_ImportModule() to 
PyRun_SimpleString().

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[issue41871] Add PyList_Remove() in listobject.c

[STINNER Victor]

STINNER Victor  added the comment:

I proposed to Hai Shi in his PR to add PyList_Remove() since I was surprised 
that the feature is exposed in Python but not at the C level.

> You always can use PyObject_CallMethod(). It is not a method called in tight 
> loop for which the overhead of calling method is significant.

He reimplemented the function by copying items into a new list except of the 
item which should be removed.

I expect that PyList_SetSlice() is more efficient than creating a new list, it 
modifies the list in-place.

I'm fine with rejecting this issue.

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[issue41871] Add PyList_Remove() in listobject.c

[hai shi]

hai shi  added the comment:

> You always can use PyObject_CallMethod(). It is not a method called in tight 
> loop for which the overhead of calling method is significant.
Thanks, serhiy. You are right.
To PR19069, it's fine to use `PyList_SetSlice` or `PyObject_CallMethod`.
We don't have the enough reason to add `PyList_Remove()`,so I decided close 
this bpo now.

PS: I attach a PR which have add `PyList_Remove` in here in case we will meet 
another appropriate user case somedays: 
https://github.com/python/cpython/compare/master...shihai1991:add_PyList_Remove?expand=1

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resolution:  -> rejected
stage:  -> resolved
status: open -> closed

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[issue41871] Add PyList_Remove() in listobject.c

[Serhiy Storchaka]

Serhiy Storchaka  added the comment:

You always can use PyObject_CallMethod(). It is not a method called in tight 
loop for which the overhead of calling method is significant.

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nosy: +serhiy.storchaka

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[issue41871] Add PyList_Remove() in listobject.c

[hai shi]

New submission from hai shi :

Do we need add PyList_Remove() in C level? same thing like list.remove().
As victor comment in: 
https://github.com/python/cpython/pull/19069#discussion_r491893466.

--
components: C API
messages: 377566
nosy: shihai1991, vstinner
priority: normal
severity: normal
status: open
title: Add PyList_Remove() in listobject.c
versions: Python 3.10

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