mimetypes on Windows should read MIME database from registry (w/patch)

[ggenellina]

BPO	4969
Nosy	@pitrou
Files	mimetypes.diff: Version 2

^{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 = None
closed_at = <Date 2009-11-15.14:26:22.545>
created_at = <Date 2009-01-17.08:58:40.600>
labels = ['type-feature', 'library']
title = 'mimetypes on Windows should read MIME database from registry (w/patch)'
updated_at = <Date 2013-03-23.12:05:36.049>
user = 'https://bugs.python.org/ggenellina'

bugs.python.org fields:

activity = <Date 2013-03-23.12:05:36.049>
actor = 'fhamand'
assignee = 'none'
closed = True
closed_date = <Date 2009-11-15.14:26:22.545>
closer = 'pitrou'
components = ['Library (Lib)']
creation = <Date 2009-01-17.08:58:40.600>
creator = 'ggenellina'
dependencies = []
files = ['15338']
hgrepos = []
issue_num = 4969
keywords = ['patch']
message_count = 6.0
messages = ['80007', '94875', '95279', '95291', '95294', '185039']
nosy_count = 5.0
nosy_names = ['ggenellina', 'pitrou', 'ocean-city', 'tercero12', 'fhamand']
pr_nums = []
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue4969'
versions = ['Python 2.7', 'Python 3.2', 'Python 3.3']

[ggenellina]

The mimetypes module has a built-in default database, and, in addition,
reads mime.types files from a list of standard places (/etc/mime.types
by example)
On Windows, those files usually don't even present; MIME information is
stored in the registry instead. Until now, the mimetypes module just
ignored those settings; this patch adds support for reading the MIME
database from the Windows registry.

[pitrou]

A couple of points:

• if the method is Windows-specific, I don't think it shouldn't bear a
  name as generic as "read_registry()". There are "registries" on other
  systems.
• the method should probably raise early on non-Windows systems (raise
  NotImplementedError?)
• please fix the coding style; don't collapse a "try", "except" or
  "finally" and the following statement on a single line
• in the tests, rather than defining an empty test case on non-Windows
  systems, make the tests skip (for example, call self.skipTest()

[ggenellina]

A new patch taking into account M. Pitrou comments:

• name changed to read_windows_registry()
• read_windows_registry() does nothing on non-Windows platforms; same
  as read_mime_types(filename) when the file does not exist.
• I hope the coding style is acceptable now
• the test is skipped on non-Windows platforms
• documentation updated
• documentation for MimeTypes.guess_all_extensions was missing; I
  added it although it isn't directly related to this issue.

[pitrou]

Thank you, the patch looks ok to me.

[pitrou]

Committed in r76306 and r76307, closing.

[fhamand]

From msg172531 in bpo-10551:

"You see, "MIME\Database\Content Type" in the Windows registry is a mime type -> file extension mapping, *not the other way around*. But read_windows_registry() tries to use it as a file extension -> mime type mapping, and bad things happen, because there are multiple mime types for certain file extensions."

This "enhancement" has basically broken the mimetypes module on windows,

e.g. On my system (windows 7 64 bit, python 3.3)
>>> mimetypes.guess_type('foo.png')
('image/x-png', None)
>>> mimetypes.guess_type('foo.jpg')
('image/pjpeg', None)

The expected results are image/png and image/jpeg

I'm having to work around this by calling mimetypes.init(files=[]) immediately after importing mimetypes to prevent it reading from the registry