Adapt media to ISBN

media/validators.py

@@ -0,0 +1,31 @@
+# -*- mode: python; coding: utf-8 -*-
+# Copyright (C) 2017-2019 by BDE ENS Paris-Saclay
+# SPDX-License-Identifier: GPL-3.0-or-later
+
+"""
+Based on https://github.com/secnot/django-isbn-field
+"""
+
+from django.core.exceptions import ValidationError
+from django.utils.translation import ugettext_lazy as _
+from six import string_types
+from stdnum import isbn
+
+
+def isbn_validator(raw_isbn):
+    """Check string is a valid ISBN number"""
+    isbn_to_check = raw_isbn.replace('-', '').replace(' ', '')
+
+    if not isinstance(isbn_to_check, string_types):
+        raise ValidationError(_(u'Invalid ISBN: Not a string'))
+
+    if len(isbn_to_check) != 10 and len(isbn_to_check) != 13:
+        raise ValidationError(_(u'Invalid ISBN: Wrong length'))
+
+    if not isbn.is_valid(isbn_to_check):
+        raise ValidationError(_(u'Invalid ISBN: Failed checksum'))
+
+    if isbn_to_check != isbn_to_check.upper():
+        raise ValidationError(_(u'Invalid ISBN: Only upper case allowed'))
+
+    return True