From 92e18aa4f0eeda3d48ea33f6399cc9130bc241ef Mon Sep 17 00:00:00 2001
From: Arthur de Jong <arthur@arthurdejong.org>
Date: Fri, 23 Jul 2010 14:46:37 +0000
Subject: add an ISSN (International Standard Serial Number) module

git-svn-id: http://arthurdejong.org/svn/python-stdnum/python-stdnum@4 9dea7c4f-944c-4273-ac1a-574ede026edc
---
 stdnum/issn.py | 57 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 57 insertions(+)
 create mode 100644 stdnum/issn.py

diff --git a/stdnum/issn.py b/stdnum/issn.py
new file mode 100644
index 0000000..1cc3a13
--- /dev/null
+++ b/stdnum/issn.py
@@ -0,0 +1,57 @@
+# issn.py - functions for handling ISSNs
+#
+# Copyright (C) 2010 Arthur de Jong
+#
+# 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 ISSNs (International Standard Serial Number), the
+standard internation code to identify serial publications.
+
+>>> validate('0024-9319')
+True
+>>> validate('0032147X') # incorrect check digit
+False
+>>> compact('0032-1478')
+'00321478'
+>>> format('00249319')
+'0024-9319'
+"""
+
+
+def compact(number):
+    """Convert the ISSN to the minimal representation. This strips the number
+    of any valid ISSN separators and removes surrounding whitespace."""
+    number = number.replace(' ','').replace('-','').strip().upper()
+    return number
+
+def _calc_check_digit(number):
+    """Calculate the ISBN check digit for 10-digit numbers. The number passed
+    should not have the check bit included."""
+    check = (11 - sum( (8 - i) * int(number[i]) for i in range(len(number)) ) ) % 11
+    return 'X' if check == 10 else str(check)
+
+def validate(number):
+    """Checks to see if the number provided is a valid ISSN. This checks
+    the length and whether the check digit is correct."""
+    number = compact(number)
+    return len(number) == 8 and \
+           number[:-1].isdigit() and \
+           _calc_check_digit(number[:-1]) == number[-1]
+
+def format(number):
+    """Reformat the passed number to the standard format."""
+    number = compact(number)
+    return number[:4] + '-' + number[4:]
-- 
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