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.

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()

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.

Thank you, the patch looks ok to me.

Committed in r76306 and r76307, closing.