[issue7232] Support of 'with' statement fo TarFile class

[Lars Gustäbel]

Changes by Lars Gustäbel :


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stage: patch review -> committed/rejected

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[issue7232] Support of 'with' statement fo TarFile class

[Lars Gustäbel]

Lars Gustäbel  added the comment:

Okay, it is done, see r78623 (trunk) and r78626 (py3k).

Thanks to all for your work and support!

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resolution:  -> accepted
status: open -> closed

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[issue7232] Support of 'with' statement fo TarFile class

[Lars Gustäbel]

Lars Gustäbel  added the comment:

I found an issue that needs to be addressed: if there is an error while the 
TarFile object is opened for writing, we cannot simply call TarFile.close() in 
the __exit__() method. close() would try to finalize the archive, i.e. write 
two zero end-of-archive blocks and a number of padding blocks.

I changed __exit__() to call close() only if everything went fine. If there was 
an exception only the most basic cleanup is done.

I added more tests and adapted the docs.

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Added file: http://bugs.python.org/file16401/issue7232.9.diff

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[issue7232] Support of 'with' statement fo TarFile class

[Lars Gustäbel]

Lars Gustäbel  added the comment:

IMO it is okay for __enter__() and __exit__() not to have docstrings.
I cannot see what's so special about the behaviour of __enter__() and 
__exit__().

__enter__() raises IOError only if the TarFile object has been already closed. 
This is exactly the behaviour I would expect, because it is the same every 
other TarFile method does when the object has been closed. IOW, using a closed 
TarFile as a context manager is the programmer's mistake, and I don't feel the 
need to document that case.

The fact that __exit__() only closes the TarFile object and does not swallow 
exceptions is what everyone expects from a "file object". It is the only 
logical thing to do, no need to document that either.

The test_context_manager_exception() test is fine. If the call to 
tarfile.open() really raises an exception then something is so terribly wrong 
and probably all of the testsuite's 200 tests will fail anyway. We can safely 
assume here that this will work, no need to double-check.

However, I have changed the docs again to be a bit more specific.

--
Added file: http://bugs.python.org/file16400/issue7232.8.diff

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[issue7232] Support of 'with' statement fo TarFile class

[Meador Inge]

Meador Inge  added the comment:

> This is common practice in the standard library.

This doesn't necessarily mean it is a correct practice :-).  All 
kidding aside, I think the assumption that the standard documentation 
on '__enter__' and '__exit__' is sufficient is a bad one.  With respect 
to how the 'tarfile' versions of these methods behave, that 
documentation is not that helpful.

In particular, the special behavior of an 'IOError' potentially being 
thrown from '__enter__' and the fact that '__exit__' does not swallow 
the exception.  These special behaviors should be documented either in 
a docstring or the library documentation.  I think this is important, 
but I may be being a bit pedantic.

Also, the last change to 'test_context_manager_exception' has a bug. 
If the call to 'tarfile.open' throws an exception, then the call to
'self.assertRaises' will swallow it.  This will cause an undefined
variable reference to 'tar' in 'self.assertTrue(tar.closed, ...)'.  I 
attached another update that fixes this problem.

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Added file: http://bugs.python.org/file16398/issue7232.7.diff

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[issue7232] Support of 'with' statement fo TarFile class

[Lars Gustäbel]

Lars Gustäbel  added the comment:

Another version of the patch (issue7232.6.diff) that checks if the TarFile 
object is still open in the __enter__() method (plus a test for that). I 
removed the docstrings as Eric suggested. This is common practice in the 
standard library.

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Added file: http://bugs.python.org/file16396/issue7232.6.diff

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[issue7232] Support of 'with' statement fo TarFile class

[Éric Araujo]

Éric Araujo  added the comment:

Hello

Minor note: I think magic methods shouldn’t have docstrings, because their name 
is enough doc (or at least enough to go read the doc). At most a one-line 
comment like “context protocol” can be useful. (The exception is __init__, 
which doesn’t have a defined set of arguments.)

Cheers

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nosy: +merwok

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[issue7232] Support of 'with' statement fo TarFile class

[Brian Curtin]

Brian Curtin  added the comment:

Good point. How about version 5? It uses base Exception in the context manager, 
which will allow us to differentiate between no exception being raised, and the 
wrong one being raised. After the context manager, we check the type of the 
exception to make sure it's correct.

I changed the exception being raised to an IOError. It could be anything, but 
given that AssertionError is what gets raised by the assert functions, it 
seemed better to avoid that one specifically. This is fairly minor, though.

If you change the "raise IOError" to be a pass statement, or another type of 
exception, you can see that the same level of information is given to you as in 
patch version 3 by Lars.

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Added file: http://bugs.python.org/file16394/issue7232.5.diff

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[issue7232] Support of 'with' statement fo TarFile class

[Meador Inge]

Meador Inge  added the comment:

> What about changing the exception test to something like what I did in > 
> issue7232.4.diff?

That is definitely more succinct, but Lars' solution provides more information 
about _why_ the test fails.  IMHO, the descriptiveness is
more important than succinctness.  Especially when debugging a failed
test.

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[issue7232] Support of 'with' statement fo TarFile class

[Meador Inge]

Meador Inge  added the comment:

Built on Brian's patch by adding the following items:

   * Added a unit test case to cover exceptional conditions.
   * Added doc strings on __enter__ and __exit__ (more consistent
 with the surrounding code).
   * Spelling error in doc update: s/manaager/manager/.
   * Link doc update to context manager type documentation (just in
 case the tarfile user is unfamiliar with context manager types).

--
nosy: +minge
Added file: http://bugs.python.org/file16367/issue7232.2.diff

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[issue7232] Support of 'with' statement fo TarFile class

[Brian Curtin]

Brian Curtin  added the comment:

The last patch does more than it should for this issue. Here is a minimal patch 
with the change, test, and doc updates.

--
Added file: http://bugs.python.org/file16307/issue7232.diff

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[issue7232] Support of 'with' statement fo TarFile class

[R. David Murray]

R. David Murray  added the comment:

Woops, I accidentally deleted one of the patch files.  Adding back.

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nosy: +r.david.murray
Added file: http://bugs.python.org/file16291/tarfileWithSupportv2.patch

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[issue7232] Support of 'with' statement fo TarFile class

[Brian Curtin]

Brian Curtin  added the comment:

Here is a patch which expands on Jaime's patch. I was converting tests for 
#7944 and looked at test_tarfile, and implemented the same feature that he did.

All places where context managers should be used in the test, they are used. 
Includes a doc update with a small example.

--
keywords: +needs review
nosy: +brian.curtin
Added file: http://bugs.python.org/file16285/issue7944_tarfile.diff

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[issue7232] Support of 'with' statement fo TarFile class

[Ezio Melotti]

Changes by Ezio Melotti :


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nosy: +ezio.melotti
priority:  -> normal
stage:  -> patch review
versions: +Python 3.2

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[issue7232] Support of 'with' statement fo TarFile class

[Jaime Buelta]

Jaime Buelta  added the comment:

I've cleaned the patch, I don't now why Eclipse added a lot of garbage,
sorry.

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Added file: http://bugs.python.org/file15221/tarfileWithSupportv2.patch

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[issue7232] Support of 'with' statement fo TarFile class

[Lars Gustäbel]

Lars Gustäbel  added the comment:

Please clean up the patch, and I take another look at it.

--
assignee:  -> lars.gustaebel
nosy: +lars.gustaebel

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[issue7232] Support of 'with' statement fo TarFile class

[Jaime Buelta]

New submission from Jaime Buelta :

Currently, the TarFile is not supporting the 'with' statement, which I
think it should for coherence with other file classes. 

I've already created a patch including it for consideration.

--
components: Library (Lib)
files: tarfileWithSupport.patch
keywords: patch
messages: 94645
nosy: jaime.buelta
severity: normal
status: open
title: Support of 'with' statement fo TarFile class
type: feature request
versions: Python 2.7
Added file: http://bugs.python.org/file15220/tarfileWithSupport.patch

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