diff --git a/pytz/__init__.py b/pytz/__init__.py

index e2f49fa..65c1d11 100644

--- a/pytz/__init__.py

+++ b/pytz/__init__.py

@@ -74,6 +74,9 @@ else:  # Python 2.x

         """

         return s.encode('ASCII')

+_tzinfo_dir = os.getenv('PYTZ_TZDATADIR') or '/usr/share/zoneinfo'

+if _tzinfo_dir.endswith(os.sep):

+    _tzinfo_dir = _tzinfo_dir[:-1]

 def open_resource(name):

     """Open a resource from the zoneinfo subdir for reading.

@@ -88,23 +91,8 @@ def open_resource(name):

     for part in name_parts:

         if part == os.path.pardir or os.path.sep in part:

             raise ValueError('Bad path segment: %r' % part)

-    zoneinfo_dir = os.environ.get('PYTZ_TZDATADIR', None)

-    if zoneinfo_dir is not None:

-        filename = os.path.join(zoneinfo_dir, *name_parts)

-    else:

-        filename = os.path.join(os.path.dirname(__file__),

-                                'zoneinfo', *name_parts)

-        if not os.path.exists(filename):

-            # http://bugs.launchpad.net/bugs/383171 - we avoid using this

-            # unless absolutely necessary to help when a broken version of

-            # pkg_resources is installed.

-            try:

-                from pkg_resources import resource_stream

-            except ImportError:

-                resource_stream = None

-

-            if resource_stream is not None:

-                return resource_stream(__name__, 'zoneinfo/' + name)

+    zoneinfo_dir = os.environ.get('PYTZ_TZDATADIR', _tzinfo_dir)

+    filename = os.path.join(zoneinfo_dir, *name_parts)

     return open(filename, 'rb')

@@ -514,1044 +502,38 @@ def _test():

 if __name__ == '__main__':

     _test()

-all_timezones = \

-['Africa/Abidjan',

- 'Africa/Accra',

- 'Africa/Addis_Ababa',

- 'Africa/Algiers',

- 'Africa/Asmara',

- 'Africa/Asmera',

- 'Africa/Bamako',

- 'Africa/Bangui',

- 'Africa/Banjul',

- 'Africa/Bissau',

- 'Africa/Blantyre',

- 'Africa/Brazzaville',

- 'Africa/Bujumbura',

- 'Africa/Cairo',

- 'Africa/Casablanca',

- 'Africa/Ceuta',

- 'Africa/Conakry',

- 'Africa/Dakar',

- 'Africa/Dar_es_Salaam',

- 'Africa/Djibouti',

- 'Africa/Douala',

- 'Africa/El_Aaiun',

- 'Africa/Freetown',

- 'Africa/Gaborone',

- 'Africa/Harare',

- 'Africa/Johannesburg',

- 'Africa/Juba',

- 'Africa/Kampala',

- 'Africa/Khartoum',

- 'Africa/Kigali',

- 'Africa/Kinshasa',

- 'Africa/Lagos',

- 'Africa/Libreville',

- 'Africa/Lome',

- 'Africa/Luanda',

- 'Africa/Lubumbashi',

- 'Africa/Lusaka',

- 'Africa/Malabo',

- 'Africa/Maputo',

- 'Africa/Maseru',

- 'Africa/Mbabane',

- 'Africa/Mogadishu',

- 'Africa/Monrovia',

- 'Africa/Nairobi',

- 'Africa/Ndjamena',

- 'Africa/Niamey',

- 'Africa/Nouakchott',

- 'Africa/Ouagadougou',

- 'Africa/Porto-Novo',

- 'Africa/Sao_Tome',

- 'Africa/Timbuktu',

- 'Africa/Tripoli',

- 'Africa/Tunis',

- 'Africa/Windhoek',

- 'America/Adak',

- 'America/Anchorage',

- 'America/Anguilla',

- 'America/Antigua',

- 'America/Araguaina',

- 'America/Argentina/Buenos_Aires',

- 'America/Argentina/Catamarca',

- 'America/Argentina/ComodRivadavia',

- 'America/Argentina/Cordoba',

- 'America/Argentina/Jujuy',

- 'America/Argentina/La_Rioja',

- 'America/Argentina/Mendoza',

- 'America/Argentina/Rio_Gallegos',

- 'America/Argentina/Salta',

- 'America/Argentina/San_Juan',

- 'America/Argentina/San_Luis',

- 'America/Argentina/Tucuman',

- 'America/Argentina/Ushuaia',

- 'America/Aruba',

- 'America/Asuncion',

- 'America/Atikokan',

- 'America/Atka',

- 'America/Bahia',

- 'America/Bahia_Banderas',

- 'America/Barbados',

- 'America/Belem',

- 'America/Belize',

- 'America/Blanc-Sablon',

- 'America/Boa_Vista',

- 'America/Bogota',

- 'America/Boise',

- 'America/Buenos_Aires',

- 'America/Cambridge_Bay',

- 'America/Campo_Grande',

- 'America/Cancun',

- 'America/Caracas',

- 'America/Catamarca',

- 'America/Cayenne',

- 'America/Cayman',

- 'America/Chicago',

- 'America/Chihuahua',

- 'America/Coral_Harbour',

- 'America/Cordoba',

- 'America/Costa_Rica',

- 'America/Creston',

- 'America/Cuiaba',

- 'America/Curacao',

- 'America/Danmarkshavn',

- 'America/Dawson',

- 'America/Dawson_Creek',

- 'America/Denver',

- 'America/Detroit',

- 'America/Dominica',

- 'America/Edmonton',

- 'America/Eirunepe',

- 'America/El_Salvador',

- 'America/Ensenada',

- 'America/Fort_Nelson',

- 'America/Fort_Wayne',

- 'America/Fortaleza',

- 'America/Glace_Bay',

- 'America/Godthab',

- 'America/Goose_Bay',

- 'America/Grand_Turk',

- 'America/Grenada',

- 'America/Guadeloupe',

- 'America/Guatemala',

- 'America/Guayaquil',

- 'America/Guyana',

- 'America/Halifax',

- 'America/Havana',

- 'America/Hermosillo',

- 'America/Indiana/Indianapolis',

- 'America/Indiana/Knox',

- 'America/Indiana/Marengo',

- 'America/Indiana/Petersburg',

- 'America/Indiana/Tell_City',

- 'America/Indiana/Vevay',

- 'America/Indiana/Vincennes',

- 'America/Indiana/Winamac',

- 'America/Indianapolis',

- 'America/Inuvik',

- 'America/Iqaluit',

- 'America/Jamaica',

- 'America/Jujuy',

- 'America/Juneau',

- 'America/Kentucky/Louisville',

- 'America/Kentucky/Monticello',

- 'America/Knox_IN',

- 'America/Kralendijk',

- 'America/La_Paz',

- 'America/Lima',

- 'America/Los_Angeles',

- 'America/Louisville',

- 'America/Lower_Princes',

- 'America/Maceio',

- 'America/Managua',

- 'America/Manaus',

- 'America/Marigot',

- 'America/Martinique',

- 'America/Matamoros',

- 'America/Mazatlan',

- 'America/Mendoza',

- 'America/Menominee',

- 'America/Merida',

- 'America/Metlakatla',

- 'America/Mexico_City',

- 'America/Miquelon',

- 'America/Moncton',

- 'America/Monterrey',

- 'America/Montevideo',

- 'America/Montreal',

- 'America/Montserrat',

- 'America/Nassau',

- 'America/New_York',

- 'America/Nipigon',

- 'America/Nome',

- 'America/Noronha',

- 'America/North_Dakota/Beulah',

- 'America/North_Dakota/Center',

- 'America/North_Dakota/New_Salem',

- 'America/Nuuk',

- 'America/Ojinaga',

- 'America/Panama',

- 'America/Pangnirtung',

- 'America/Paramaribo',

- 'America/Phoenix',

- 'America/Port-au-Prince',

- 'America/Port_of_Spain',

- 'America/Porto_Acre',

- 'America/Porto_Velho',

- 'America/Puerto_Rico',

- 'America/Punta_Arenas',

- 'America/Rainy_River',

- 'America/Rankin_Inlet',

- 'America/Recife',

- 'America/Regina',

- 'America/Resolute',

- 'America/Rio_Branco',

- 'America/Rosario',

- 'America/Santa_Isabel',

- 'America/Santarem',

- 'America/Santiago',

- 'America/Santo_Domingo',

- 'America/Sao_Paulo',

- 'America/Scoresbysund',

- 'America/Shiprock',

- 'America/Sitka',

- 'America/St_Barthelemy',

- 'America/St_Johns',

- 'America/St_Kitts',

- 'America/St_Lucia',

- 'America/St_Thomas',

- 'America/St_Vincent',

- 'America/Swift_Current',

- 'America/Tegucigalpa',

- 'America/Thule',

- 'America/Thunder_Bay',

- 'America/Tijuana',

- 'America/Toronto',

- 'America/Tortola',

- 'America/Vancouver',

- 'America/Virgin',

- 'America/Whitehorse',

- 'America/Winnipeg',

- 'America/Yakutat',

- 'America/Yellowknife',

- 'Antarctica/Casey',

- 'Antarctica/Davis',

- 'Antarctica/DumontDUrville',

- 'Antarctica/Macquarie',

- 'Antarctica/Mawson',

- 'Antarctica/McMurdo',

- 'Antarctica/Palmer',

- 'Antarctica/Rothera',

- 'Antarctica/South_Pole',

- 'Antarctica/Syowa',

- 'Antarctica/Troll',

- 'Antarctica/Vostok',

- 'Arctic/Longyearbyen',

- 'Asia/Aden',

- 'Asia/Almaty',

- 'Asia/Amman',

- 'Asia/Anadyr',

- 'Asia/Aqtau',

- 'Asia/Aqtobe',

- 'Asia/Ashgabat',

- 'Asia/Ashkhabad',

- 'Asia/Atyrau',

- 'Asia/Baghdad',

- 'Asia/Bahrain',

- 'Asia/Baku',

- 'Asia/Bangkok',

- 'Asia/Barnaul',

- 'Asia/Beirut',

- 'Asia/Bishkek',

- 'Asia/Brunei',

- 'Asia/Calcutta',

- 'Asia/Chita',

- 'Asia/Choibalsan',

- 'Asia/Chongqing',

- 'Asia/Chungking',

- 'Asia/Colombo',

- 'Asia/Dacca',

- 'Asia/Damascus',

- 'Asia/Dhaka',

- 'Asia/Dili',

- 'Asia/Dubai',

- 'Asia/Dushanbe',

- 'Asia/Famagusta',

- 'Asia/Gaza',

- 'Asia/Harbin',

- 'Asia/Hebron',

- 'Asia/Ho_Chi_Minh',

- 'Asia/Hong_Kong',

- 'Asia/Hovd',

- 'Asia/Irkutsk',

- 'Asia/Istanbul',

- 'Asia/Jakarta',

- 'Asia/Jayapura',

- 'Asia/Jerusalem',

- 'Asia/Kabul',

- 'Asia/Kamchatka',

- 'Asia/Karachi',

- 'Asia/Kashgar',

- 'Asia/Kathmandu',

- 'Asia/Katmandu',

- 'Asia/Khandyga',

- 'Asia/Kolkata',

- 'Asia/Krasnoyarsk',

- 'Asia/Kuala_Lumpur',

- 'Asia/Kuching',

- 'Asia/Kuwait',

- 'Asia/Macao',

- 'Asia/Macau',

- 'Asia/Magadan',

- 'Asia/Makassar',

- 'Asia/Manila',

- 'Asia/Muscat',

- 'Asia/Nicosia',

- 'Asia/Novokuznetsk',

- 'Asia/Novosibirsk',

- 'Asia/Omsk',

- 'Asia/Oral',

- 'Asia/Phnom_Penh',

- 'Asia/Pontianak',

- 'Asia/Pyongyang',

- 'Asia/Qatar',

- 'Asia/Qostanay',

- 'Asia/Qyzylorda',

- 'Asia/Rangoon',

- 'Asia/Riyadh',

- 'Asia/Saigon',

- 'Asia/Sakhalin',

- 'Asia/Samarkand',

- 'Asia/Seoul',

- 'Asia/Shanghai',

- 'Asia/Singapore',

- 'Asia/Srednekolymsk',

- 'Asia/Taipei',

- 'Asia/Tashkent',

- 'Asia/Tbilisi',

- 'Asia/Tehran',

- 'Asia/Tel_Aviv',

- 'Asia/Thimbu',

- 'Asia/Thimphu',

- 'Asia/Tokyo',

- 'Asia/Tomsk',

- 'Asia/Ujung_Pandang',

- 'Asia/Ulaanbaatar',

- 'Asia/Ulan_Bator',

- 'Asia/Urumqi',

- 'Asia/Ust-Nera',

- 'Asia/Vientiane',

- 'Asia/Vladivostok',

- 'Asia/Yakutsk',

- 'Asia/Yangon',

- 'Asia/Yekaterinburg',

- 'Asia/Yerevan',

- 'Atlantic/Azores',

- 'Atlantic/Bermuda',

- 'Atlantic/Canary',

- 'Atlantic/Cape_Verde',

- 'Atlantic/Faeroe',

- 'Atlantic/Faroe',

- 'Atlantic/Jan_Mayen',

- 'Atlantic/Madeira',

- 'Atlantic/Reykjavik',

- 'Atlantic/South_Georgia',

- 'Atlantic/St_Helena',

- 'Atlantic/Stanley',

- 'Australia/ACT',

- 'Australia/Adelaide',

- 'Australia/Brisbane',

- 'Australia/Broken_Hill',

- 'Australia/Canberra',

- 'Australia/Currie',

- 'Australia/Darwin',

- 'Australia/Eucla',

- 'Australia/Hobart',

- 'Australia/LHI',

- 'Australia/Lindeman',

- 'Australia/Lord_Howe',

- 'Australia/Melbourne',

- 'Australia/NSW',

- 'Australia/North',

- 'Australia/Perth',

- 'Australia/Queensland',

- 'Australia/South',

- 'Australia/Sydney',

- 'Australia/Tasmania',

- 'Australia/Victoria',

- 'Australia/West',

- 'Australia/Yancowinna',

- 'Brazil/Acre',

- 'Brazil/DeNoronha',

- 'Brazil/East',

- 'Brazil/West',

- 'CET',

- 'CST6CDT',

- 'Canada/Atlantic',

- 'Canada/Central',

- 'Canada/Eastern',

- 'Canada/Mountain',

- 'Canada/Newfoundland',

- 'Canada/Pacific',

- 'Canada/Saskatchewan',

- 'Canada/Yukon',

- 'Chile/Continental',

- 'Chile/EasterIsland',

- 'Cuba',

- 'EET',

- 'EST',

- 'EST5EDT',

- 'Egypt',

- 'Eire',

- 'Etc/GMT',

- 'Etc/GMT+0',

- 'Etc/GMT+1',

- 'Etc/GMT+10',

- 'Etc/GMT+11',

- 'Etc/GMT+12',

- 'Etc/GMT+2',

- 'Etc/GMT+3',

- 'Etc/GMT+4',

- 'Etc/GMT+5',

- 'Etc/GMT+6',

- 'Etc/GMT+7',

- 'Etc/GMT+8',

- 'Etc/GMT+9',

- 'Etc/GMT-0',

- 'Etc/GMT-1',

- 'Etc/GMT-10',

- 'Etc/GMT-11',

- 'Etc/GMT-12',

- 'Etc/GMT-13',

- 'Etc/GMT-14',

- 'Etc/GMT-2',

- 'Etc/GMT-3',

- 'Etc/GMT-4',

- 'Etc/GMT-5',

- 'Etc/GMT-6',

- 'Etc/GMT-7',

- 'Etc/GMT-8',

- 'Etc/GMT-9',

- 'Etc/GMT0',

- 'Etc/Greenwich',

- 'Etc/UCT',

- 'Etc/UTC',

- 'Etc/Universal',

- 'Etc/Zulu',

- 'Europe/Amsterdam',

- 'Europe/Andorra',

- 'Europe/Astrakhan',

- 'Europe/Athens',

- 'Europe/Belfast',

- 'Europe/Belgrade',

- 'Europe/Berlin',

- 'Europe/Bratislava',

- 'Europe/Brussels',

- 'Europe/Bucharest',

- 'Europe/Budapest',

- 'Europe/Busingen',

- 'Europe/Chisinau',

- 'Europe/Copenhagen',

- 'Europe/Dublin',

- 'Europe/Gibraltar',

- 'Europe/Guernsey',

- 'Europe/Helsinki',

- 'Europe/Isle_of_Man',

- 'Europe/Istanbul',

- 'Europe/Jersey',

- 'Europe/Kaliningrad',

- 'Europe/Kiev',

- 'Europe/Kirov',

- 'Europe/Lisbon',

- 'Europe/Ljubljana',

- 'Europe/London',

- 'Europe/Luxembourg',

- 'Europe/Madrid',

- 'Europe/Malta',

- 'Europe/Mariehamn',

- 'Europe/Minsk',

- 'Europe/Monaco',

- 'Europe/Moscow',

- 'Europe/Nicosia',

- 'Europe/Oslo',

- 'Europe/Paris',

- 'Europe/Podgorica',

- 'Europe/Prague',

- 'Europe/Riga',

- 'Europe/Rome',

- 'Europe/Samara',

- 'Europe/San_Marino',

- 'Europe/Sarajevo',

- 'Europe/Saratov',

- 'Europe/Simferopol',

- 'Europe/Skopje',

- 'Europe/Sofia',

- 'Europe/Stockholm',

- 'Europe/Tallinn',

- 'Europe/Tirane',

- 'Europe/Tiraspol',

- 'Europe/Ulyanovsk',

- 'Europe/Uzhgorod',

- 'Europe/Vaduz',

- 'Europe/Vatican',

- 'Europe/Vienna',

- 'Europe/Vilnius',

- 'Europe/Volgograd',

- 'Europe/Warsaw',

- 'Europe/Zagreb',

- 'Europe/Zaporozhye',

- 'Europe/Zurich',

- 'GB',

- 'GB-Eire',

- 'GMT',

- 'GMT+0',

- 'GMT-0',

- 'GMT0',

- 'Greenwich',

- 'HST',

- 'Hongkong',

- 'Iceland',

- 'Indian/Antananarivo',

- 'Indian/Chagos',

- 'Indian/Christmas',

- 'Indian/Cocos',

- 'Indian/Comoro',

- 'Indian/Kerguelen',

- 'Indian/Mahe',

- 'Indian/Maldives',

- 'Indian/Mauritius',

- 'Indian/Mayotte',

- 'Indian/Reunion',

- 'Iran',

- 'Israel',

- 'Jamaica',

- 'Japan',

- 'Kwajalein',

- 'Libya',

- 'MET',

- 'MST',

- 'MST7MDT',

- 'Mexico/BajaNorte',

- 'Mexico/BajaSur',

- 'Mexico/General',

- 'NZ',

- 'NZ-CHAT',

- 'Navajo',

- 'PRC',

- 'PST8PDT',

- 'Pacific/Apia',

- 'Pacific/Auckland',

- 'Pacific/Bougainville',

- 'Pacific/Chatham',

- 'Pacific/Chuuk',

- 'Pacific/Easter',

- 'Pacific/Efate',

- 'Pacific/Enderbury',

- 'Pacific/Fakaofo',

- 'Pacific/Fiji',

- 'Pacific/Funafuti',

- 'Pacific/Galapagos',

- 'Pacific/Gambier',

- 'Pacific/Guadalcanal',

- 'Pacific/Guam',

- 'Pacific/Honolulu',

- 'Pacific/Johnston',

- 'Pacific/Kiritimati',

- 'Pacific/Kosrae',

- 'Pacific/Kwajalein',

- 'Pacific/Majuro',

- 'Pacific/Marquesas',

- 'Pacific/Midway',

- 'Pacific/Nauru',

- 'Pacific/Niue',

- 'Pacific/Norfolk',

- 'Pacific/Noumea',

- 'Pacific/Pago_Pago',

- 'Pacific/Palau',

- 'Pacific/Pitcairn',

- 'Pacific/Pohnpei',

- 'Pacific/Ponape',

- 'Pacific/Port_Moresby',

- 'Pacific/Rarotonga',

- 'Pacific/Saipan',

- 'Pacific/Samoa',

- 'Pacific/Tahiti',

- 'Pacific/Tarawa',

- 'Pacific/Tongatapu',

- 'Pacific/Truk',

- 'Pacific/Wake',

- 'Pacific/Wallis',

- 'Pacific/Yap',

- 'Poland',

- 'Portugal',

- 'ROC',

- 'ROK',

- 'Singapore',

- 'Turkey',

- 'UCT',

- 'US/Alaska',

- 'US/Aleutian',

- 'US/Arizona',

- 'US/Central',

- 'US/East-Indiana',

- 'US/Eastern',

- 'US/Hawaii',

- 'US/Indiana-Starke',

- 'US/Michigan',

- 'US/Mountain',

- 'US/Pacific',

- 'US/Samoa',

- 'UTC',

- 'Universal',

- 'W-SU',

- 'WET',

- 'Zulu']

+

+all_timezones = []

+for root, dirs, files in os.walk(_tzinfo_dir):

+    for exclude in 'posix', 'right':

+        if exclude in dirs:

+            del dirs[dirs.index(exclude)]

+

+    all_timezones.extend(os.path.join(root, tz_file)[len(_tzinfo_dir)+1:]

+            for tz_file in files

+            if tz_file not in ['leapseconds', 'README', 'Theory']

+            and '.' not in tz_file)

+

 all_timezones = LazyList(

         tz for tz in all_timezones if resource_exists(tz))

 all_timezones_set = LazySet(all_timezones)

-common_timezones = \

-['Africa/Abidjan',

- 'Africa/Accra',

- 'Africa/Addis_Ababa',

- 'Africa/Algiers',

- 'Africa/Asmara',

- 'Africa/Bamako',

- 'Africa/Bangui',

- 'Africa/Banjul',

- 'Africa/Bissau',

- 'Africa/Blantyre',

- 'Africa/Brazzaville',

- 'Africa/Bujumbura',

- 'Africa/Cairo',

- 'Africa/Casablanca',

- 'Africa/Ceuta',

- 'Africa/Conakry',

- 'Africa/Dakar',

- 'Africa/Dar_es_Salaam',

- 'Africa/Djibouti',

- 'Africa/Douala',

- 'Africa/El_Aaiun',

- 'Africa/Freetown',

- 'Africa/Gaborone',

- 'Africa/Harare',

- 'Africa/Johannesburg',

- 'Africa/Juba',

- 'Africa/Kampala',

- 'Africa/Khartoum',

- 'Africa/Kigali',

- 'Africa/Kinshasa',

- 'Africa/Lagos',

- 'Africa/Libreville',

- 'Africa/Lome',

- 'Africa/Luanda',

- 'Africa/Lubumbashi',

- 'Africa/Lusaka',

- 'Africa/Malabo',

- 'Africa/Maputo',

- 'Africa/Maseru',

- 'Africa/Mbabane',

- 'Africa/Mogadishu',

- 'Africa/Monrovia',

- 'Africa/Nairobi',

- 'Africa/Ndjamena',

- 'Africa/Niamey',

- 'Africa/Nouakchott',

- 'Africa/Ouagadougou',

- 'Africa/Porto-Novo',

- 'Africa/Sao_Tome',

- 'Africa/Tripoli',

- 'Africa/Tunis',

- 'Africa/Windhoek',

- 'America/Adak',

- 'America/Anchorage',

- 'America/Anguilla',

- 'America/Antigua',

- 'America/Araguaina',

- 'America/Argentina/Buenos_Aires',

- 'America/Argentina/Catamarca',

- 'America/Argentina/Cordoba',

- 'America/Argentina/Jujuy',

- 'America/Argentina/La_Rioja',

- 'America/Argentina/Mendoza',

- 'America/Argentina/Rio_Gallegos',