Add update_constants command to setup.py

It retrieves and parses attributes.pot and countries.pot files
from transifex to extract various constants needed in Picard.
It helps to keep those in sync with MusicBrainz website.

It then generates:
- picard/attributes.py containing cover art types, medium formats, and release group types
- picard/countries.py containing countries

`update_constants` command replaces `update_countries`

setup.py

@@ -424,8 +424,8 @@ def _get_option_name(obj):
     raise Exception("No such command class")
 
 
-class picard_update_countries(Command):
-    description = "Regenerate countries.py"
+class picard_update_constants(Command):
+    description = "Regenerate attributes.py and countries.py"
     user_options = [
         ('skip-pull', None, "skip the tx pull steps"),
     ]
@@ -443,22 +443,22 @@ class picard_update_countries(Command):
 
         from babel.messages import pofile
 
-        countries = dict()
         if not self.skip_pull:
             txpull_cmd = [
                 tx_executable,
                 'pull',
                 '--force',
-                '--resource=musicbrainz.countries',
+                '--resource=musicbrainz.attributes,musicbrainz.countries',
                 '--source',
                 '--language=none',
             ]
             self.spawn(txpull_cmd)
 
-        potfile = os.path.join('po', 'countries', 'countries.pot')
+        countries = dict()
+        countries_potfile = os.path.join('po', 'countries', 'countries.pot')
         isocode_comment = u'iso.code:'
-        with open(potfile, 'rb') as f:
-            log.info('Parsing %s' % potfile)
+        with open(countries_potfile, 'rb') as f:
+            log.info('Parsing %s' % countries_potfile)
             po = pofile.read_po(f)
             for message in po:
                 if not message.id or not isinstance(message.id, unicode):
@@ -472,6 +472,28 @@ class picard_update_countries(Command):
             else:
                 sys.exit('Failed to extract any country code/name !')
 
+        attributes = dict()
+        attributes_potfile = os.path.join('po', 'attributes', 'attributes.pot')
+        extract_attributes = (
+            u'DB:cover_art_archive.art_type/name',
+            u'DB:medium_format/name',
+            u'DB:release_group_primary_type/name',
+            u'DB:release_group_secondary_type/name',
+        )
+        with open(attributes_potfile, 'rb') as f:
+            log.info('Parsing %s' % attributes_potfile)
+            po = pofile.read_po(f)
+            for message in po:
+                if not message.id or not isinstance(message.id, unicode):
+                    continue
+                for loc, pos in message.locations:
+                    if loc in extract_attributes:
+                        attributes[u"%s:%03d" % (loc,pos)] = message.id
+            if attributes:
+                self.attributes_py_file(attributes)
+            else:
+                sys.exit('Failed to extract any attribute !')
+
     def countries_py_file(self, countries):
         header = (u"# -*- coding: utf-8 -*-\n"
                   u"# Automatically generated - don't edit.\n"
@@ -492,6 +514,26 @@ class picard_update_countries(Command):
             log.info("%s was rewritten (%d countries)" % (filename,
                                                           len(countries)))
 
+    def attributes_py_file(self, attributes):
+        header = (u"# -*- coding: utf-8 -*-\n"
+                  u"# Automatically generated - don't edit.\n"
+                  u"# Use `python setup.py {option}` to update it.\n"
+                  u"\n"
+                  u"MB_ATTRIBUTES = {{\n")
+        line   =  u"    u'{key}': u'{value}',\n"
+        footer =  u"}}\n"
+        filename = os.path.join('picard', 'attributes.py')
+        with open(filename, 'w') as attributes_py:
+            def write_utf8(s, **kwargs):
+                attributes_py.write(s.format(**kwargs).encode('utf-8'))
+
+            write_utf8(header, option=_get_option_name(self))
+            for key, value in sorted(attributes.items(), key=lambda (k,v): k):
+                write_utf8(line, key=key, value=value.replace("'", "\\'"))
+            write_utf8(footer)
+            log.info("%s was rewritten (%d attributes)" % (filename,
+                                                          len(attributes)))
+
 
 def cflags_to_include_dirs(cflags):
     cflags = cflags.split()
@@ -507,6 +549,7 @@ def _picard_get_locale_files():
     path_domain = {
         'po': 'picard',
         os.path.join('po', 'countries'): 'picard-countries',
+        os.path.join('po', 'attributes'): 'picard-attributes',
     }
     for path, domain in path_domain.iteritems():
         for filepath in glob.glob(os.path.join(path, '*.po')):
@@ -537,7 +580,7 @@ args2 = {
         'clean_ui': picard_clean_ui,
         'install': picard_install,
         'install_locales': picard_install_locales,
-        'update_countries': picard_update_countries,
+        'update_constants': picard_update_constants,
         'get_po_files': picard_get_po_files,
         'regen_pot_file': picard_regen_pot_file,
     },