From 57c12d816bcf324b14cb2dc7f8b284400c075591 Mon Sep 17 00:00:00 2001
From: Arthur de Jong <arthur@arthurdejong.org>
Date: Sat, 15 Apr 2017 21:20:05 +0200
Subject: An ISMN can only be 10 or 13 digits

This also adds the test that an ISMN should start with 9790.
---
 stdnum/ismn.py          |  8 ++++++--
 tests/test_ismn.doctest | 20 +++++++++++++++++---
 2 files changed, 23 insertions(+), 5 deletions(-)

diff --git a/stdnum/ismn.py b/stdnum/ismn.py
index 3de83f1..b04c763 100644
--- a/stdnum/ismn.py
+++ b/stdnum/ismn.py
@@ -1,6 +1,6 @@
 # ismn.py - functions for handling ISMNs
 #
-# Copyright (C) 2010, 2011, 2012, 2013 Arthur de Jong
+# Copyright (C) 2010-2017 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
@@ -62,8 +62,12 @@ def validate(number):
         if number[0] != 'M':
             raise InvalidFormat()
         ean.validate('9790' + number[1:])
-    else:
+    elif len(number) == 13:
+        if not number.startswith('9790'):
+            raise InvalidComponent()
         ean.validate(number)
+    else:
+        raise InvalidLength()
     return number
 
 
diff --git a/tests/test_ismn.doctest b/tests/test_ismn.doctest
index c3d46b6..23eb5f2 100644
--- a/tests/test_ismn.doctest
+++ b/tests/test_ismn.doctest
@@ -1,6 +1,6 @@
 test_ismn.doctest - more detailed doctests for stdnum.ismn module
 
-Copyright (C) 2010, 2011, 2012, 2013 Arthur de Jong
+Copyright (C) 2010-2017 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
@@ -41,7 +41,7 @@ These are normal variations that should just work.
 '9790260000438'
 
 
-Tests for mangling and incorect check digits.
+Tests for mangling and incorrect check digits.
 
 >>> ismn.validate('979-0-3217-6543-x')
 Traceback (most recent call last):
@@ -54,7 +54,7 @@ InvalidChecksum: ...
 >>> ismn.validate('979M321765450')
 Traceback (most recent call last):
     ...
-InvalidFormat: ...
+InvalidComponent: ...
 >>> ismn.validate('Z-3217-6546-8')
 Traceback (most recent call last):
     ...
@@ -72,6 +72,7 @@ See if 10 to 13 digit conversion works.
 
 
 Test the ismn_type() function
+
 >>> ismn.ismn_type('M-3217-6546-7')
 'ISMN10'
 >>> ismn.ismn_type('BAD')
@@ -85,3 +86,16 @@ Regrouping tests.
 '979-0-3217-6546-7'
 >>> ismn.format('9790321765450')
 '979-0-3217-6545-0'
+
+
+While an EAN can also be less than 13 digits and ISMN should always be
+13 digits (when not 10 digits) and start with 9790.
+
+>>> ismn.validate('979023456784')
+Traceback (most recent call last):
+    ...
+InvalidLength: ...
+>>> ismn.validate('9781234567866')
+Traceback (most recent call last):
+    ...
+InvalidComponent: ...
-- 
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