Opening File according to mime type

Most of the modern desktops already have a command line utility to open file according to their mime type (GNOME/gnome-open, OSX/open, Windows/start, XFCE/exo-open, KDE/kfmclient ...)

However, most (all?) of them rely on the file extension, where I needed something to view attachments from mutt. Which passes the file data in stdin.

So, here we go (I call this attview):

#!/usr/bin/env python
'''View attachment with right application'''

__author__ = "Miki Tebeka <miki.tebeka@gmail.com>"

from os import popen, system
from os.path import isfile
import re

class ViewError(Exception):
   pass

def view_attachment(data):
    # In the .destop file, the file name is %u or %U
    u_sub = re.compile("%u", re.I).sub

    FILENAME = "/tmp/attview"
    fo = open(FILENAME, "wb")
    fo.write(data)
    fo.close()

    mime_type = popen("file -ib %s" % FILENAME).read().strip()
    if ";" in mime_type:
        mime_type = mime_type[:mime_type.find(";")]
    if mime_type == "application/x-not-regular-file":
        raise ViewError("can't guess mime type")

    APPS_DIR = "/usr/share/applications"
    for line in open("%s/defaults.list" % APPS_DIR):
        if line.startswith(mime_type):
            mime, appfile = line.strip().split("=")
            break
    else:
        raise ViewError("can't find how to open %s" % mime_type)

    appfile = "%s/%s" % (APPS_DIR, appfile)
    if not isfile(appfile):
        raise ViewError("can't find %s" % appfile)
    for line in open(appfile):
        line = line.strip()
        if line.startswith("Exec"):
            key, cmd = line.split("=")
            fullcmd = u_sub(FILENAME, cmd)
            if fullcmd == cmd:
                fullcmd += " %s" % FILENAME
            system(fullcmd + "&")
            break
    else:
        raise ViewError("can't find Exec in %s" % appfile)


def main(argv=None):
    from sys import stdin
    if argv is None:
        import sys
        argv = sys.argv

    from optparse import OptionParser

    parser = OptionParser("usage: %prog [FILENAME]")

    opts, args = parser.parse_args(argv[1:])
    if len(args) not in (0, 1):
        parser.error("wrong number of arguments") # Will exit

    filename = args[0] if args else "-"

    if filename == "-":
        data = stdin.read()
    else:
        try:
            data = open(filename, "rb").read()
        except IOError, e:
            raise SystemExit("error: %s" % e.strerror)

    try:
        view_attachment(data)
    except ViewError, e:
        raise SystemExit("error: %s" % e)

if __name__ == "__main__":
    main()