Add CAS Registry Number

stdnum/cas.py

@@ -0,0 +1,82 @@
+# cas.py - functions for handling CAS registry numbers
+#
+# Copyright (C) 2022 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
+
+"""CAS Registry Number.
+
+A CAS Registry Number, CAS RN or CAS number is a unique identified assign to
+chemical substances. The number is issued by the Chemical Abstracts Service
+(CAS).
+
+The number consists of 5 to 10 digits and is assigned sequentially and
+contains a check digit.
+
+More information:
+
+* https://en.wikipedia.org/wiki/CAS_Registry_Number
+* https://www.cas.org/cas-data/cas-registry
+
+>>> validate('12770-26-2')
+'12770-26-2'
+>>> validate('12770-29-2')
+Traceback (most recent call last):
+    ...
+InvalidChecksum: ...
+>>> validate('012770-26-2')
+Traceback (most recent call last):
+    ...
+InvalidFormat: ...
+"""
+
+import re
+
+from stdnum.exceptions import *
+from stdnum.util import clean
+
+
+_cas_re = re.compile(r'^[1-9][0-9]{1,6}-[0-9]{2}-[0-9]$')
+
+
+def compact(number):
+    """Convert the number to the minimal representation."""
+    return clean(number).strip()
+
+
+def calc_check_digit(number):
+    """Calculate the check digit. The number passed should not have the check
+    digit included."""
+    number = clean(number, '-').strip()
+    return str(sum((i + 1) * int(n) for i, n in enumerate(reversed(number))) % 10)
+
+
+def validate(number):
+    """Check if the number is a valid CAS Registry Number."""
+    number = compact(number)
+    if not _cas_re.match(number):
+        raise InvalidFormat()
+    if not number[-1] == calc_check_digit(number[:-1]):
+        raise InvalidChecksum()
+    return number
+
+
+def is_valid(number):
+    """Check if the number is a valid CAS Registry Number."""
+    try:
+        return bool(validate(number))
+    except ValidationError:
+        return False