glib 's gstrfuncs.c

has:

 G_CONST_RETURN gchar *
 g_strip_context  (const gchar *msgid, 
		  const gchar *msgval)
 {
  if (msgval == msgid)
    {
      const char *c = strchr (msgid, '|');
      if (c != NULL)
	return c + 1;
    }

  return msgval;
 }

which is defined as #define Q_(String) g_strip_context ((String), gettext (String))

now this is done in python this way (apart from the | check which I did not implement):

 def Q_(s):
   s = _(s)
   if s[0] == '?':
       s = s[s.find(':')+1:] # remove ?abc: part
   return s

Now some theory..

in your code you do:

 menu.name = Q_('?vcard:Unknown')
 special.name = Q_('?os:Unknown') 

so pot will have:

 #: vcard.py:123 
 msgid "?vcard:Unknown" 
 msgstr "" 

 #: vcard.py:126
 msgid "?os:Unknown" 
 msgstr ""

translators get the idea how to translate Unknown and then can either do their translation either by including the ?zzz: part or without

this helps them so then now the context but moreover the know that gender (masculine, feminine, neutral)

thanks to piman, nkour