Mailcap Fix

Note: An official fix for this issue was released in Python 3.6.0. This package now acts as a backport for all older versions of python.

Summary

This package patches the python standard library's mailcap module in order to correctly handle windcard entries.

The bug is documented on the bug tracker here: issue 14977

Installation

$ pip install mailcap-fix

Example

Consider a mailcap file that contains the following two lines

image/*; feh %s
image/jpeg; eog %s

Because the image/* entry is defined first, it should take precedence over the image/jpeg entry when searching for a match. This behavior is defined by RFC 1524. However, the standard library's implementation will always evaluate wildcard entries last.

Before

>>> import mailcap
>>> d = mailcap.getcaps()
>>> # Incorrectly returns the second entry
>>> mailcap.findmatch(d, 'image/jpeg', filename='test.jpg')
('eog test.jpg', {'view': 'eog %s'})

After

>>> from mailcap_fix import mailcap
>>> d = mailcap.getcaps()
>>> # Correctly returns the wildcard entry
>>> mailcap.findmatch(d, 'image/jpeg', filename='test.jpg')
('feh test.jpg', {'view': 'feh %s', 'lineno': 0})

How it works

The goal of this patch is to conform to RFCC 1524, while preserving as much backwards compatibility as possible and without adding any "magic".

mailcap_fix adds a new field lineno to each entry in the mailcap dict. This line number is then used to sort entries in descending order when searching for a match. For backwards compatability, if lineno is not present entries will simply not be sorted. Because RFC 1524 defines a whitelist of valid mailcap fieldnames, the addition of lineno should not conflict with any other mailcap fields.

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