tarfile module does not correctly choose compression algorithms

[wdv4758h]

BPO	23421
Nosy	@berkerpeksag, @serhiy-storchaka
Files	fix_compressions_dict.patch: fix compressions dict in tarfile module add_tarfile_cli_filetype_test.patch: tests for tarfile CLI add_tarfile_cli_filetype_test_refactor.patch: fix compressions dict in tarfile module (refactored)

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = 'https://github.com/serhiy-storchaka'
closed_at = <Date 2015-02-10.06:49:38.549>
created_at = <Date 2015-02-09.13:03:37.079>
labels = ['type-bug', 'library']
title = 'tarfile module does not correctly choose compression algorithms'
updated_at = <Date 2015-02-10.06:49:38.548>
user = 'https://bugs.python.org/wdv4758h'

bugs.python.org fields:

activity = <Date 2015-02-10.06:49:38.548>
actor = 'serhiy.storchaka'
assignee = 'serhiy.storchaka'
closed = True
closed_date = <Date 2015-02-10.06:49:38.549>
closer = 'serhiy.storchaka'
components = ['Library (Lib)']
creation = <Date 2015-02-09.13:03:37.079>
creator = 'wdv4758h'
dependencies = []
files = ['38056', '38059', '38079']
hgrepos = ['297', '298', '299']
issue_num = 23421
keywords = ['patch']
message_count = 11.0
messages = ['235604', '235606', '235608', '235609', '235611', '235623', '235626', '235668', '235669', '235671', '235672']
nosy_count = 4.0
nosy_names = ['python-dev', 'berker.peksag', 'serhiy.storchaka', 'wdv4758h']
pr_nums = []
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue23421'
versions = ['Python 3.4', 'Python 3.5']

[wdv4758h]

The command "python -m tarfile -c test.tar.bz2 test/" should create a file that is compressed by bzip2,
but actually the detection of compression algorithm that should be used is broken (for gz, xz, bz2).

fix it by prepending a dot to the keys of the dictionary

[serhiy-storchaka]

Thank you for your patch. Could you provide tests?

[wdv4758h]

yes

just wanna know is there a standard way to get file type by libmagic ?

[serhiy-storchaka]

No need to use libmagic. tarfile.TarFile.gzopen() should fail if the file is not gzipped tar file. There CLI tests in Lib/test/test_tarfile.py. New test should create tar file with file name that ends with the '.gz' extension and check that it can be open and read with gzopen().

[wdv4758h]

Oh, I can use it.
thx

[wdv4758h]

Here is the tests.

[serhiy-storchaka]

In general LGTM, but I have added few nitpicks on Rietveld.

[wdv4758h]

Attached factored patch for tests.

It looks much better. :)

[wdv4758h]

s/factored/refactored/

[python-dev]

New changeset 2a06379f6562 by Serhiy Storchaka in branch '3.4':
Issue bpo-23421: Fixed compression in tarfile CLI. Patch by wdv4758h.
https://hg.python.org/cpython/rev/2a06379f6562

New changeset 5b70eb1cfad0 by Serhiy Storchaka in branch 'default':
Issue bpo-23421: Fixed compression in tarfile CLI. Patch by wdv4758h.
https://hg.python.org/cpython/rev/5b70eb1cfad0

[serhiy-storchaka]

Thank you for your contribution.