Format UK phone number with area code

phone_format.py

#!/usr/local/bin/python3

import re
import sys

area_codes = [
    '020', '023', '024', '028', '029', '0113',
    '0114', '0115', '0116', '0117', '0118', '0121',
    '0131', '0141', '0151', '0161', '0191', '01200',
    '01202', '01204', '01205', '01206', '01207', '01208',
    '01209', '01223', '01224', '01225', '01226', '01227',
    '01228', '01229', '01233', '01234', '01235', '01236',
    '01237', '01239', '01241', '01242', '01243', '01244',
    '01245', '01246', '01248', '01249', '01250', '01252',
    '01253', '01254', '01255', '01256', '01257', '01258',
    '01259', '01260', '01261', '01262', '01263', '01264',
    '01267', '01268', '01269', '01270', '01271', '01273',
    '01274', '01275', '01276', '01277', '01278', '01279',
    '01280', '01282', '01283', '01284', '01285', '01286',
    '01287', '01288', '01289', '01290', '01291', '01292',
    '01293', '01294', '01295', '01296', '01297', '01298',
    '01299', '01300', '01301', '01302', '01303', '01304',
    '01305', '01306', '01307', '01308', '01309', '01320',
    '01322', '01323', '01324', '01325', '01326', '01327',
    '01328', '01329', '01330', '01332', '01333', '01334',
    '01335', '01337', '01339', '01340', '01341', '01342',
    '01343', '01344', '01346', '01347', '01348', '01349',
    '01350', '01352', '01353', '01354', '01355', '01356',
    '01357', '01358', '01359', '01360', '01361', '01362',
    '01363', '01364', '01366', '01367', '01368', '01369',
    '01371', '01372', '01373', '01375', '01376', '01377',
    '01379', '01380', '01381', '01382', '01383', '01384',
    '01386', '01387', '01388', '01389', '01392', '01394',
    '01395', '01397', '01398', '01400', '01403', '01404',
    '01405', '01406', '01407', '01408', '01409', '01420',
    '01422', '01423', '01424', '01425', '01427', '01428',
    '01429', '01430', '01431', '01432', '01433', '01434',
    '01435', '01436', '01437', '01438', '01439', '01440',
    '01442', '01443', '01444', '01445', '01446', '01449',
    '01450', '01451', '01452', '01453', '01454', '01455',
    '01456', '01457', '01458', '01460', '01461', '01462',
    '01463', '01464', '01465', '01466', '01467', '01469',
    '01470', '01471', '01472', '01473', '01474', '01475',
    '01476', '01477', '01478', '01479', '01480', '01481',
    '01482', '01483', '01484', '01485', '01487', '01488',
    '01489', '01490', '01491', '01492', '01493', '01494',
    '01495', '01496', '01497', '01499', '01501', '01502',
    '01503', '01505', '01506', '01507', '01508', '01509',
    '01520', '01522', '01524', '01525', '01526', '01527',
    '01528', '01529', '01530', '01531', '01534', '01535',
    '01536', '01538', '01539', '01540', '01542', '01543',
    '01544', '01545', '01546', '01547', '01548', '01549',
    '01550', '01553', '01554', '01555', '01556', '01557',
    '01558', '01559', '01560', '01561', '01562', '01563',
    '01564', '01565', '01566', '01567', '01568', '01569',
    '01570', '01571', '01572', '01573', '01575', '01576',
    '01577', '01578', '01579', '01580', '01581', '01582',
    '01583', '01584', '01586', '01588', '01590', '01591',
    '01592', '01593', '01594', '01595', '01597', '01598',
    '01599', '01600', '01603', '01604', '01606', '01608',
    '01609', '01620', '01621', '01622', '01623', '01624',
    '01625', '01626', '01628', '01629', '01630', '01631',
    '01633', '01634', '01635', '01636', '01637', '01638',
    '01639', '01641', '01642', '01643', '01644', '01646',
    '01647', '01650', '01651', '01652', '01653', '01654',
    '01655', '01656', '01659', '01661', '01663', '01664',
    '01665', '01666', '01667', '01668', '01669', '01670',
    '01671', '01672', '01673', '01674', '01675', '01676',
    '01677', '01678', '01680', '01681', '01683', '01684',
    '01685', '01686', '01687', '01688', '01689', '01690',
    '01691', '01692', '01694', '01695', '01697', '01698',
    '01700', '01702', '01704', '01706', '01707', '01708',
    '01709', '01720', '01721', '01722', '01723', '01724',
    '01725', '01726', '01727', '01728', '01729', '01730',
    '01732', '01733', '01736', '01737', '01738', '01740',
    '01743', '01744', '01745', '01746', '01747', '01748',
    '01749', '01750', '01751', '01752', '01753', '01754',
    '01756', '01757', '01758', '01759', '01760', '01761',
    '01763', '01764', '01765', '01766', '01767', '01768',
    '01769', '01770', '01771', '01772', '01773', '01775',
    '01776', '01777', '01778', '01779', '01780', '01782',
    '01784', '01785', '01786', '01787', '01788', '01789',
    '01790', '01792', '01793', '01794', '01795', '01796',
    '01797', '01798', '01799', '01803', '01805', '01806',
    '01807', '01808', '01809', '01821', '01822', '01823',
    '01824', '01825', '01827', '01828', '01829', '01830',
    '01832', '01833', '01834', '01835', '01837', '01838',
    '01840', '01841', '01842', '01843', '01844', '01845',
    '01847', '01848', '01851', '01852', '01854', '01855',
    '01856', '01857', '01858', '01859', '01862', '01863',
    '01864', '01865', '01866', '01869', '01870', '01871',
    '01872', '01873', '01874', '01875', '01876', '01877',
    '01878', '01879', '01880', '01882', '01883', '01884',
    '01885', '01886', '01887', '01888', '01889', '01890',
    '01892', '01895', '01896', '01899', '01900', '01902',
    '01903', '01904', '01905', '01908', '01909', '01920',
    '01922', '01923', '01924', '01925', '01926', '01928',
    '01929', '01931', '01932', '01933', '01934', '01935',
    '01937', '01938', '01939', '01942', '01943', '01944',
    '01945', '01946', '01947', '01948', '01949', '01950',
    '01951', '01952', '01953', '01954', '01955', '01957',
    '01959', '01962', '01963', '01964', '01967', '01968',
    '01969', '01970', '01971', '01972', '01974', '01975',
    '01977', '01978', '01980', '01981', '01982', '01983',
    '01984', '01985', '01986', '01987', '01988', '01989',
    '01992', '01993', '01994', '01995', '01997', '013873',
    '015242', '015394', '015395', '015396', '016973', '016974',
    '017683', '017684', '017687', '019467'
    ]


def break_number(string):
    if len(string) < 6: return string
    front_length = len(string) // 2
    return string[:front_length] + '-' + string[front_length:]


input_text = sys.stdin.read()
digits = re.sub(r'\D', '', input_text)
if not 10 <= len(digits) <= 11:
    print("Please double-check the phone number. It's an unusual length.",
          file=sys.stderr)

for code in sorted(area_codes, key=len, reverse=True):
    if digits.startswith(code):
        print('({area}) {number}'.format(
            area=code,
            number=break_number(digits[len(code):])
            ))
        break
else:
    print(digits[:5], break_number(digits[5:]))

Rewritten and improved as a simple JavaScript tool here: https://bitbucket.org/robjwells/ms-phone-format-js