[issue19829] _pyio.BufferedReader and _pyio.TextIOWrapper destructor don't emit ResourceWarning if the file is not closed

[STINNER Victor]

STINNER Victor  added the comment:

While it would be great to also emit ResourceWarning, in the last 8 years, 
nobody managed to implement the feature. Also, this issue has no activity. I 
prefer to close the issue.

--
resolution:  -> out of date
stage: needs patch -> resolved
status: open -> closed

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[issue19829] _pyio.BufferedReader and _pyio.TextIOWrapper destructor don't emit ResourceWarning if the file is not closed

[Serhiy Storchaka]

Serhiy Storchaka added the comment:

> Serhiy: why did you add 2.7 to this bug? For 2.7, I don’t think anything 
> should be done. There is no ResourceWarning in 2.7.

Just for the case.

Not calling close() in __del__() is one option, and it looks attractive. But 
there are possible hidden catches. There is no guarantee that flush() writes 
all buffered data, some stateful encoder or compressor can left some data in 
the buffer unless explicitly closed. close() can write required footer or close 
connection. If not call close() in __del__(), GzipFile will produce incorrect 
file.

May be this is appropriate. This is why explicit close() should be called or 
context manager should be used.

Other option is to use some API through all closable objects. _dealloc_warn() 
is not the only option.

1. Add an optional parameter to close() methods to denote that it is called 
from __del__. This is backward incompatible option, it is too late to do this.

2. __del__() calls special method instead of close() if exists.

3. The _dealloc_warn() option (the name should be changed). The wrapper 
delegates emitting a warning to wrapped object by calling the _dealloc_warn() 
method if exists. Unlike to previous option this method is called in addition 
to close(), not instead.

4. The wrapper checks special attribute (or calls a method) of wrapped object. 
If it exists and is true, the wrapper emits a warning.

--
nosy: +benjamin.peterson, stutzbach
versions:  -Python 2.7

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[issue19829] _pyio.BufferedReader and _pyio.TextIOWrapper destructor don't emit ResourceWarning if the file is not closed

[Martin Panter]

Martin Panter added the comment:

In the long term, I prefer not calling close() in __del__(), like 
del-flush.patch, although I admit it is an API change and should probably be 
limited to 3.6+. If people want to improve things in 3.5, privately 
implementing _dealloc_warn() like Victor’s pyio_res_warn-3.patch seems the best 
option.

Serhiy: why did you add 2.7 to this bug? For 2.7, I don’t think anything should 
be done. There is no ResourceWarning in 2.7.

In 3.5, _dealloc_warn() could also be implemented in SocketIO (possibly also 
HTTPResponse, GzipFile, etc). But it should not become a public API, and I 
don’t think it is important to make this sort of change to 3.5 anyway.

In 3.6, if we stopped __del__() from calling close() like del-flush.patch, we 
would be changing the documented behaviour: 
 says “IOBase . 
. . calls the instance’s close() method.” But the end result seems cleaner to 
me. I think changing or adding an API (__del__, _dealloc_warn, etc) is 
necessary for a general solution to the problem.

The effect of del-flush.patch will be that a wrapped FileIO or similar object 
will not be closed until all references are deleted.

>>> file = open(os.devnull, "wb", 0)
>>> print(file)
<_io.FileIO name='/dev/null' mode='wb' closefd=True>
>>> wrapper = BufferedWriter(file)

In 3.5, deleting the wrapper produces a warning and closes the underlying file:

>>> del wrapper
__main__:1: ResourceWarning: unclosed file <_io.BufferedWriter name='/dev/null'>
>>> print(file)
<_io.FileIO [closed]>
>>> file.write(b"more data")
Traceback (most recent call last):
  File "", line 1, in 
ValueError: I/O operation on closed file

I propose that in 3.6, deleting a wrapper should not automatically close or 
warn about the wrapped object until all references are deleted:

>>> del wrapper  # No problem; we still have a reference to "file"
>>> file.write(b"more data")  # File is still open
9
>>> del file  # Finally closes the file and triggers the warning
ResourceWarning: unclosed file 

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[issue19829] _pyio.BufferedReader and _pyio.TextIOWrapper destructor don't emit ResourceWarning if the file is not closed

[Serhiy Storchaka]

Serhiy Storchaka added the comment:

1. What if only object which directly owns a limited resource will emit a 
ResourceWarning? This can break some tests, but may be these tests are too 
strong? Current GC may be better than when io classes were implemented.

2. An object which indirectly owns a limited resource don't know about this if 
use only public API. It can known about this only if the wrapped object 
provides _dealloc_warn(). Thus _dealloc_warn() extends the API. If allows an 
object which indirectly owns a limited resource emit a resource warning, it may 
be worth to expose _dealloc_warn() or something equivalent as public API.

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[issue19829] _pyio.BufferedReader and _pyio.TextIOWrapper destructor don't emit ResourceWarning if the file is not closed

[STINNER Victor]

STINNER Victor added the comment:

Ok, I now understand the problem better. They are two kinds of io objects:

(1) object which directly or indirectly owns a limited resource like file 
descriptor => must emit a ResourceWarning
(2) object which don't own a limited resource => no ResourceWarning must be 
logged

Examples of (1): FileIO, BufferedReader(FileIO), 
TextIOWrapper(BufferedReader(FileIO))

Examples of (2): BytesIO, BuffereadReader(BytesIO), 
TextIOWrapper(BuffereadReader(BytesIO))


The tricky part is to decide if an object owns a limited resource or not. 
Currently, the io module uses the _dealloc_warn() trick. A close() method tries 
to call _dealloc_warn(), but it ignores any exception when calling 
_dealloc_warn(). BufferedReader calls raw._dealloc_warn(). TextIOWrapper calls 
buffer._dealloc_warn().


For case (1), BufferedReader(FileIO).close() calls FileIO._dealloc_warn() => 
ResourceWarning is logged

For case (2), BufferedReader(BytesIO).close() calls BytesIO._dealloc_warn() 
raises an AttributeError => no warning is logged


Well, we can call this a hack, but it works :-) pyio_res_warn-3.patch 
implements the same hack in _pyio.

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[issue19829] _pyio.BufferedReader and _pyio.TextIOWrapper destructor don't emit ResourceWarning if the file is not closed

[STINNER Victor]

STINNER Victor added the comment:

> For io.BytesIO, I fixed the code to inherit correctly IOBase finalizer.

Oh, I forgot to include it in my patch. But it's maybe better to have it in a 
different patch: see attached bytesio_stringio.patch which changes also 
io.StringIO to inherit the IOBase finalizer.

Emitting a ResourceWarning in io.BytesIO and io.StringIO adds a *lot* of 
warnings when running the Python test suite. Since these objects only contain 
memory, no very limited resource like file descriptors, it's probably better to 
*not* log ResourceWarning for them.

--
Added file: http://bugs.python.org/file42292/bytesio_stringio.patch

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[issue19829] _pyio.BufferedReader and _pyio.TextIOWrapper destructor don't emit ResourceWarning if the file is not closed

[STINNER Victor]

STINNER Victor added the comment:

> I think we should use one of Martin's option. If there are any issues with 
> garbage collecting, we should fix the garbage collector.

Ok, here is a new simpler proposition: remove all _dealloc_warn() method, and 
simply emit the ResourceWarning in IOBase finalizer.

With this change, all objects which inherit from io.IOBase (or _pyio.IOBase) 
now emits a ResourceWarning if they are not closed explicitly. You have to 
override the __del__() method to prevent this warning.

A lot of new objects start to log ResourceWarning: io.SocketIO, 
_pyio.TextIOWrapper, io.BytesIO, http.client.HTTPResponse, etc.

For io.BytesIO, I fixed the code to inherit correctly IOBase finalizer.

--

A lot of tests start to fail because they emit a lot of ResourceWarning 
warnings. I don't know yet if it's a feature or a bug :-)

--

With the patch, Python starts to logs warnings like:

sys:1: ResourceWarning: unclosed file <_io.TextIOWrapper name='' 
mode='w' encoding='UTF-8'>
sys:1: ResourceWarning: unclosed file <_io.TextIOWrapper name='' 
mode='r' encoding='UTF-8'>

You can use my patch of the issue #26642 to fix these warnings.

ResourceWarning is emited even if FileIO.closefd is false.

Note: It looks like the ResourceWarning is not always displayed. Yet another 
bug?

--
Added file: http://bugs.python.org/file42291/iobase_finalizer.patch

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[issue19829] _pyio.BufferedReader and _pyio.TextIOWrapper destructor don't emit ResourceWarning if the file is not closed

[STINNER Victor]

STINNER Victor added the comment:

> I don't like _dealloc_warn() at all. It looks as a dirty hack and doesn't 
> work with custom file-like objects.

I tried to support emitting a ResourceWarning when the close() method is 
overriden in a subclass, but then I saw that io doesn't support this use case 
neither:
---
import io
import os

class MyFile(io.FileIO):
def close(self):
os.close(self.fileno())

f = MyFile('/etc/issue')
f = None
---
=> no warning

Ok, now I have to read again Martin's patches since I didn't understand them at 
the first read :-)

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[issue19829] _pyio.BufferedReader and _pyio.TextIOWrapper destructor don't emit ResourceWarning if the file is not closed

[Serhiy Storchaka]

Serhiy Storchaka added the comment:

I don't like _dealloc_warn() at all. It looks as a dirty hack and doesn't work 
with custom file-like objects.

I think we should use one of Martin's option. If there are any issues with 
garbage collecting, we should fix the garbage collector.

--
versions: +Python 3.5, Python 3.6 -Python 3.3, Python 3.4

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[issue19829] _pyio.BufferedReader and _pyio.TextIOWrapper destructor don't emit ResourceWarning if the file is not closed

[STINNER Victor]

STINNER Victor added the comment:

Try attached res_warn.py script to test manually all ResourceWarning warnings.

Ouput of python3.6 -Wd res_warn.py:
--
text
<_pyio.TextIOWrapper name='/etc/issue' mode='r' encoding='UTF-8'>
res_warn.py:9: ResourceWarning: unclosed file <_pyio.FileIO name='/etc/issue' 
mode='rb' closefd=True>
  f = None

buffered
<_pyio.BufferedReader name='/etc/issue'>
res_warn.py:15: ResourceWarning: unclosed file <_pyio.FileIO name='/etc/issue' 
mode='rb' closefd=True>
  f=None

raw
<_pyio.FileIO name='/etc/issue' mode='rb' closefd=True>
res_warn.py:21: ResourceWarning: unclosed file <_pyio.FileIO name='/etc/issue' 
mode='rb' closefd=True>
  f=None

fileio
<_pyio.FileIO name='/etc/issue' mode='rb' closefd=True>
res_warn.py:27: ResourceWarning: unclosed file <_pyio.FileIO name='/etc/issue' 
mode='rb' closefd=True>
  f=None

--


Ouput of python3.6 -X tracemalloc=2 -Wd res_warn.py:
--
text
<_pyio.TextIOWrapper name='/etc/issue' mode='r' encoding='UTF-8'>
res_warn.py:9: ResourceWarning: unclosed file <_pyio.FileIO name='/etc/issue' 
mode='rb' closefd=True>
  f = None
Object allocated at (most recent call first):
  File "/home/haypo/prog/python/default/Lib/_pyio.py", lineno 209
closefd, opener=opener)
  File "res_warn.py", lineno 7
f = _pyio.open(fn, "r")

buffered
<_pyio.BufferedReader name='/etc/issue'>
res_warn.py:15: ResourceWarning: unclosed file <_pyio.FileIO name='/etc/issue' 
mode='rb' closefd=True>
  f=None
Object allocated at (most recent call first):
  File "/home/haypo/prog/python/default/Lib/_pyio.py", lineno 209
closefd, opener=opener)
  File "res_warn.py", lineno 13
f = _pyio.open(fn, "rb")

raw
<_pyio.FileIO name='/etc/issue' mode='rb' closefd=True>
res_warn.py:21: ResourceWarning: unclosed file <_pyio.FileIO name='/etc/issue' 
mode='rb' closefd=True>
  f=None
Object allocated at (most recent call first):
  File "/home/haypo/prog/python/default/Lib/_pyio.py", lineno 209
closefd, opener=opener)
  File "res_warn.py", lineno 19
f = _pyio.open(fn, "rb", 0)

fileio
<_pyio.FileIO name='/etc/issue' mode='rb' closefd=True>
res_warn.py:27: ResourceWarning: unclosed file <_pyio.FileIO name='/etc/issue' 
mode='rb' closefd=True>
  f=None
Object allocated at (most recent call first):
  File "res_warn.py", lineno 25
f = _pyio.FileIO(fn, "rb")

--

--
Added file: http://bugs.python.org/file42274/res_warn.py

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[issue19829] _pyio.BufferedReader and _pyio.TextIOWrapper destructor don't emit ResourceWarning if the file is not closed

[STINNER Victor]

STINNER Victor added the comment:

del-detach.patch: I don't understand the change in _pyio.py. I think that the 
change on socket.py is no more need since the change 46329eec5515 (issue 
#26590).

del-flush.patch:
* change on IOBase.__del__() change the behaviour compared to the io module, I 
don't think that it's correct. I may also break backward compatibility :-/
* change on fileio.c implements a finalizer for FileIO: io.IOBase already 
implements a finalizer which calls close(), I'm not sure that this change is 
needed?
* change on iobase.c removes io.IOBase finalizer. I don't understand this. It 
breaks ResourceWarning on io.Buffered* and io.TextIOWrapper classes, no?

Well, I guess that these two patches were written before Serhiy reimplemented 
the FileIO in pure Python, and this change outdated your two patches.

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[issue19829] _pyio.BufferedReader and _pyio.TextIOWrapper destructor don't emit ResourceWarning if the file is not closed

[STINNER Victor]

STINNER Victor added the comment:

Oh, the io module is more complex than what I expected :-) test_io fails with 
pyio_res_warn-2.patch.

test_io now pass with pyio_res_warn-3.patch. I fixed FileIO.close() to always 
call super().close(), and set self._fd to -1 even if logging the 
ResourceWarning raised an exception.

--
Added file: http://bugs.python.org/file42273/pyio_res_warn-3.patch

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[issue19829] _pyio.BufferedReader and _pyio.TextIOWrapper destructor don't emit ResourceWarning if the file is not closed

[STINNER Victor]

STINNER Victor added the comment:

(oops, there was a typo in my first patch)

--
Added file: http://bugs.python.org/file42272/pyio_res_warn-2.patch

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[issue19829] _pyio.BufferedReader and _pyio.TextIOWrapper destructor don't emit ResourceWarning if the file is not closed

[STINNER Victor]

Changes by STINNER Victor :


Removed file: http://bugs.python.org/file42271/pyio_res_warn.patch

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[issue19829] _pyio.BufferedReader and _pyio.TextIOWrapper destructor don't emit ResourceWarning if the file is not closed

[STINNER Victor]

STINNER Victor added the comment:

Attached patch modifies _pyio to mimick better the reference io module:

* Add IOBase._finalizing
* IOBase.__del__() sets _finalizing to True
* Add FileIO._dealloc_warn()
* Remove FileIO.__del__()
* FileIO.close(), _BufferedIOMixin.close() and TextIOWrapper.close() now calls 
_dealloc_warn() if _finalizing is true
* Override closed() method in FileIO: needed because FileIO.close() now calls 
super().close() before logging the ResourceWarning, and the file is expected to 
see open in the warning
* FileIO.close() now calls super().close() *before* closing the file descriptor

I added hasattr(.., '_dealloc_warn') sanity checks because _dealloc_warn() are 
added to concrete classes, not to base classes.

--
Added file: http://bugs.python.org/file42271/pyio_res_warn.patch

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[issue19829] _pyio.BufferedReader and _pyio.TextIOWrapper destructor don't emit ResourceWarning if the file is not closed

[Martin Panter]

Martin Panter added the comment:

It looks like the C _io close() implementations delegate to the wrapped 
object’s undocumented _dealloc_warn() method to emit the warning if 
“self-finalizing” is set. For wrapped objects like BytesIO that do not have 
it, I guess the error due to the missing method is ignored.

There is no Python implementation of FileIO yet (see Issue 21859), so the 
Python file wrapper classes still use the C FileIO implementation, which emits 
a resource warning. However for the wrapper classes, _pyio.IOBase.__del__() 
explicitly invokes the wrapper’s close() method, which will invoke 
FileIO.close() method, which bypasses the warning.

Similarly, any object inheriting from the C implmentation’s _io.IOBase will 
also have close() explicitly invoked when being finalized, bypassing any 
warnings of the underlying wrapped object. The SocketIO instances returned by 
socket.makefile() are an example of this.

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[issue19829] _pyio.BufferedReader and _pyio.TextIOWrapper destructor don't emit ResourceWarning if the file is not closed

[Martin Panter]

Martin Panter added the comment:

One option would be for any wrapper-type class (e.g. BufferedReader, SocketIO) 
to override __del__(). Instead of calling close(), it should call detach() or 
equivalent, and delete the returned reference to the underlying wrapped object 
without explicitly closing it, to allow a warning to be generated. Maybe a 
WrappedIO mixin class could help with this.

I am posting del-detach.patch which roughly implements the above option. It 
only seems to break the test_override_destructor() tests for the 
TextIOWrapperTest and CommonBufferedTests classes, which expect close() to be 
called.

Another more radical option might be to make IOBase.__del__() only call 
flush(), not close(), except for the actual implementations that really should 
emit a warning, like FileIO. I will have a go at doing this option in another 
patch.

Both these options would change the behaviour in some cases that rely on the 
garbage collector to close objects. They would defer the automatic closing 
until all references of the underlying object are garbage collected, instead of 
just when the wrapped object is garbage collected. A third option would be to 
add explicit __del__() methods emitting a warning in each class, along with any 
exception supression needed due to Python interpreter finalization quirks.

--
keywords: +patch
Added file: http://bugs.python.org/file38134/del-detach.patch

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[issue19829] _pyio.BufferedReader and _pyio.TextIOWrapper destructor don't emit ResourceWarning if the file is not closed

[Martin Panter]

Changes by Martin Panter vadmium...@gmail.com:


Removed file: http://bugs.python.org/file38135/del-flush.patch

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[issue19829] _pyio.BufferedReader and _pyio.TextIOWrapper destructor don't emit ResourceWarning if the file is not closed

[Martin Panter]

Martin Panter added the comment:

Posting del-flush.patch, which only calls flush() instead of close() from 
__del__(), except for the FileIO class. Quick analysis of resulting test 
failures:

These tests fail because they are obviously written to test that __del__ calls 
close():
* IOTest.test_IOBase_destructor
* IOTest.test_RawIOBase_destructor
* IOTest.test_BufferedIOBase_destructor
* IOTest.test_TextIOBase_destructor
* test_override_destructor as mentioned above

CBufferedReader/Writer/RandomTest.test_garbage_collection() fail because they 
do not free the reference to the wrapped raw file object. Similarly, 
CTextIOWrapperTest.test_garbage_collection() holds references to both levels of 
wrapped object.

TextIOWrapperTest.test_destructor() fails because it assumes the wrapped 
close() will be called. The data is still written to the wrapped file though.

MiscIOTest.test_warn_on_dealloc/_fd() fail because the warning message only 
refers to the FileIO object rather than the wrapper object.

--
Added file: http://bugs.python.org/file38135/del-flush.patch

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[issue19829] _pyio.BufferedReader and _pyio.TextIOWrapper destructor don't emit ResourceWarning if the file is not closed

[Martin Panter]

Changes by Martin Panter vadmium...@gmail.com:


Added file: http://bugs.python.org/file38136/del-flush.patch

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[issue19829] _pyio.BufferedReader and _pyio.TextIOWrapper destructor don't emit ResourceWarning if the file is not closed

[Akira Li]

Akira Li added the comment:

Related issue21859 Add Python implementation of FileIO

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[issue19829] _pyio.BufferedReader and _pyio.TextIOWrapper destructor don't emit ResourceWarning if the file is not closed

[Martin Panter]

Changes by Martin Panter vadmium...@gmail.com:


--
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[issue19829] _pyio.BufferedReader and _pyio.TextIOWrapper destructor don't emit ResourceWarning if the file is not closed

[STINNER Victor]

New submission from STINNER Victor:

$ ./python
Python 3.4.0b1 (default:acabd3f035fe, Nov 28 2013, 15:04:09) 
[GCC 4.8.2 20131017 (Red Hat 4.8.2-1)] on linux
Type help, copyright, credits or license for more information.
 import _pyio
 f=_pyio.open(/etc/issue); f=None
 f=_pyio.open(/etc/issue, rb); f=None
 f=_pyio.open(/etc/issue, rb, 0); f=None
__main__:1: ResourceWarning: unclosed file _io.FileIO name='/etc/issue' 
mode='rb'
 import io
 f=io.open(/etc/issue); f=None
__main__:1: ResourceWarning: unclosed file _io.TextIOWrapper name='/etc/issue' 
mode='r' encoding='UTF-8'
 f=io.open(/etc/issue, rb); f=None
__main__:1: ResourceWarning: unclosed file _io.BufferedReader 
name='/etc/issue'
 f=io.open(/etc/issue, rb, 0); f=None
__main__:1: ResourceWarning: unclosed file _io.FileIO name='/etc/issue' 
mode='rb'

I expect the same behaviour when I use _pyio or io module.

--
messages: 204714
nosy: haypo, pitrou
priority: normal
severity: normal
status: open
title: _pyio.BufferedReader and _pyio.TextIOWrapper destructor don't emit 
ResourceWarning if the file is not closed
versions: Python 3.3, Python 3.4

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[issue19829] _pyio.BufferedReader and _pyio.TextIOWrapper destructor don't emit ResourceWarning if the file is not closed

[Serhiy Storchaka]

Changes by Serhiy Storchaka storch...@gmail.com:


--
nosy: +serhiy.storchaka

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[issue19829] _pyio.BufferedReader and _pyio.TextIOWrapper destructor don't emit ResourceWarning if the file is not closed

[Serhiy Storchaka]

Serhiy Storchaka added the comment:

I think it will be good.

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components: +IO
stage:  - needs patch
type:  - resource usage
versions: +Python 2.7

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[issue19829] _pyio.BufferedReader and _pyio.TextIOWrapper destructor don't emit ResourceWarning if the file is not closed

[Arfrever Frehtes Taifersar Arahesis]

Changes by Arfrever Frehtes Taifersar Arahesis arfrever@gmail.com:


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nosy: +Arfrever

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