Index: python-stdnum/stdnum/fi/__init__.py
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Index: python-stdnum/stdnum/fi/hetu.py
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--- python-stdnum/stdnum/fi/hetu.py	(revision 0)
+++ python-stdnum/stdnum/fi/hetu.py	(working copy)
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+# hetu.py - functions for handling Finnish personal identity codes
+# coding: utf-8
+#
+# Copyright (C) 2011 Jussi Judin
+#
+# This library is free software; you can redistribute it and/or
+# modify it under the terms of the GNU Lesser General Public
+# License as published by the Free Software Foundation; either
+# version 2.1 of the License, or (at your option) any later version.
+#
+# This library is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+# Lesser General Public License for more details.
+#
+# You should have received a copy of the GNU Lesser General Public
+# License along with this library; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+# 02110-1301 USA
+
+"""Module for handling Finnish personal identity codes (HETU, Henkilötunnus).
+
+See http://www.vaestorekisterikeskus.fi/default.aspx?id=45 for checksum
+calculation details and http://tarkistusmerkit.teppovuori.fi/tarkmerk.htm#hetu1
+for historical details.
+
+>>> is_valid('131052-308T')
+True
+>>> is_valid('131052+308T')
+True
+>>> is_valid('131052A308T')
+True
+>>> is_valid('131052a308t')
+True
+
+Invalid checksum:
+>>> is_valid('131052-308U')
+False
+
+Invalid century sign:
+>>> is_valid('131052/308T')
+False
+
+Invalid century sign:
+>>> is_valid('131052T308T')
+False
+
+Invalid birth date:
+>>> is_valid('310252-308Y')
+False
+>>> is_valid('130052-308R')
+False
+
+Leaving first zero out:
+>>> is_valid('10101-0101')
+False
+
+Invalid individual number:
+>>> is_valid('131052-000V')
+False
+
+>>> compact('131052a308t')
+'131052A308T'
+>>> format('131052a308t')
+'131052A308T'
+"""
+
+import re
+import datetime
+
+def _normalize(number):
+    result = number.strip()
+    result = result.upper()
+    return result
+
+# These are here just for completeness as there are no different length forms
+# of Finnish personal identity codes:
+compact = _normalize
+format = _normalize
+
+_centuries = {
+    '+': 1800,
+    '-': 1900,
+    'A': 2000,
+    }
+
+# Finnish personal identity codes are composed of date part, century indicating
+# sign, individual number and control character.
+# ddmmyyciiiC
+_hetu_re = re.compile("^(?P<day>[0123]\d)(?P<month>[01]\d)(?P<year>\d\d)(?P<century>[\-+A])(?P<individual>\d\d\d)(?P<control>[0-9ABCDEFHJKLMNPRSTUVWXY])$")
+
+_control_characters = "0123456789ABCDEFHJKLMNPRSTUVWXY"
+
+def _calc_checksum(number):
+    return _control_characters[number % 31]
+
+def is_valid(number):
+    normalized = _normalize(number)
+
+    match = _hetu_re.search(normalized)
+    if not match:
+        return False
+
+    century_code = match.group("century")
+    if century_code not in _centuries:
+        return False
+    century = _centuries[century_code]
+
+    day = int(match.group("day"))
+    month = int(match.group("month"))
+    year = int(match.group("year"))
+    date_year = century + year
+
+    # Check if birth date is valid.
+    try:
+        datetime.date(date_year, month, day)
+    except ValueError, e:
+        return False
+
+    individual_id = int(match.group("individual"))
+    # For historical reasons individual IDs start from 002.
+    if individual_id < 2:
+        return False
+
+    checkable_number = int("%02d%02d%02d%03d" % (day, month, year, individual_id))
+    claimed_control_character = match.group("control")
+    calculated_control_character = _calc_checksum(checkable_number)
+    if claimed_control_character != calculated_control_character:
+        return False
+
+    return True