allow argparse FileType to accept encoding and errors arguments

[bethard]

BPO	11175
Nosy	@amauryfa, @ezio-melotti, @merwok, @cjerdonek, @akheron
Files	filetype11175.patch: patch filetype11175.patch filetype11175.patch filetype11175.patch

^{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/akheron'
closed_at = <Date 2012-12-15.20:46:16.690>
created_at = <Date 2011-02-10.15:47:13.087>
labels = ['easy', 'type-feature', 'library']
title = 'allow argparse FileType to accept encoding and errors arguments'
updated_at = <Date 2012-12-17.07:41:25.024>
user = 'https://bugs.python.org/bethard'

bugs.python.org fields:

activity = <Date 2012-12-17.07:41:25.024>
actor = 'lum'
assignee = 'petri.lehtinen'
closed = True
closed_date = <Date 2012-12-15.20:46:16.690>
closer = 'petri.lehtinen'
components = ['Library (Lib)']
creation = <Date 2011-02-10.15:47:13.087>
creator = 'bethard'
dependencies = []
files = ['27674', '27729', '28139', '28195']
hgrepos = []
issue_num = 11175
keywords = ['patch', 'easy', 'needs review']
message_count = 18.0
messages = ['128301', '128310', '128318', '173599', '173603', '173611', '173851', '173852', '176403', '176404', '176414', '176464', '176472', '176479', '176829', '177561', '177562', '177638']
nosy_count = 8.0
nosy_names = ['amaury.forgeotdarc', 'bethard', 'ezio.melotti', 'eric.araujo', 'chris.jerdonek', 'python-dev', 'petri.lehtinen', 'lum']
pr_nums = []
priority = 'low'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue11175'
versions = ['Python 3.4']

[bethard]

Suggestion from a personal email:

Allow FileType to accept encoding and errors arguments
and pass these as keyword arguments to codecs.open() instead of open().

[amauryfa]

The encoding and errors arguments are probably useful, but why would you use the codecs module?

[bethard]

Probably because the suggestion came from someone thinking about both Python 2 and 3. But given that this feature request can only target Python 3.3, you're absolutely right that there's no need to go through the codecs module.

[lum]

Here's an attempt at implementing this (my first contribution). Some notes:

• I tried to keep __repr__() backwards compatible. It would have been easier to inherit from _AttributeHolder, but maybe this might break some things...
• I added some test cases for __repr__(), but that's it. I don't think there's any other sensible test to do, as we're really just passing stuff to open()
• not sure about the style, especially line breaks...

[akheron]

Lucas: You only added tests for the repr, you should probably test the actual new functionality, too.

[lum]

OK, as discussed offline with Petri I'll put some tests to ensure that open() is called the right way (using unittest.mock.patch).

[lum]

Alright, here's a version with more tests (unittest.mock is awesome!). I think it tests exactly what it should (and no more), i.e. that the arguments are correctly passed to open.

[akheron]

LGTM. Let's wait for Steven's comments as he's the maintainer of argparse.

[lum]

Is there something I can do something to move this forward?

[akheron]

Since Steven is not responding, I think I can commit it at some point. Thanks for the remainder :)

[cjerdonek]

The patch needs documentation, though, right?

http://docs.python.org/dev/library/argparse.html#filetype-objects