Add support for Mauritius TIN

Fixes arthurdejong#356

stdnum/mu/__init__.py

@@ -2,6 +2,7 @@
 # coding: utf-8
 #
 # Copyright (C) 2018 Arthur de Jong
+# Copyright (C) 2023 Leandro Regueiro
 #
 # This library is free software; you can redistribute it and/or
 # modify it under the terms of the GNU Lesser General Public
@@ -19,3 +20,6 @@
 # 02110-1301 USA
 
 """Collection of Mauritian numbers."""
+
+# provide aliases
+from stdnum.mu import tan as vat  # noqa: F401

stdnum/mu/tan.py

@@ -0,0 +1,78 @@
+# tan.py - functions for handling Mauritius TAN numbers
+# coding: utf-8
+#
+# Copyright (C) 2023 Leandro Regueiro
+#
+# 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
+
+"""TAN (Tax Account Number, Mauritius tax number).
+
+This number consists of 8 digits. For individuals the first digit is always 1,
+5, 7 or 8. For entities the first digit is always 2 or 3.
+
+More information:
+
+* https://www.oecd.org/tax/automatic-exchange/crs-implementation-and-assistance/tax-identification-numbers/Mauritius-TIN.pdf
+
+>>> validate('20405553')
+'20405553'
+>>> validate('12345')
+Traceback (most recent call last):
+    ...
+InvalidLength: ...
+>>> format('20405553')
+'20405553'
+"""  # noqa: E501
+
+from stdnum.exceptions import *
+from stdnum.util import clean, isdigits
+
+
+def compact(number):
+    """Convert the number to the minimal representation.
+
+    This strips the number of any valid separators and removes surrounding
+    whitespace.
+    """
+    return clean(number, ' -').strip()
+
+
+def validate(number):
+    """Check if the number is a valid Mauritius TAN number.
+
+    This checks the length and formatting.
+    """
+    number = compact(number)
+    if len(number) != 8:
+        raise InvalidLength()
+    if not isdigits(number):
+        raise InvalidFormat()
+    if number[0] not in ('1', '2', '3', '5', '7', '8'):
+        raise InvalidComponent()
+    return number
+
+
+def is_valid(number):
+    """Check if the number is a valid Mauritius TAN number."""
+    try:
+        return bool(validate(number))
+    except ValidationError:
+        return False
+
+
+def format(number):
+    """Reformat the number to the standard presentation format."""
+    return compact(number)

tests/test_mu_tan.doctest

@@ -0,0 +1,57 @@
+test_mu_tan.doctest - more detailed doctests for stdnum.mu.tan module
+
+Copyright (C) 2023 Leandro Regueiro
+
+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
+
+
+This file contains more detailed doctests for the stdnum.mu.tan module. It
+tries to test more corner cases and detailed functionality that is not really
+useful as module documentation.
+
+>>> from stdnum.mu import tan
+
+
+Tests for some corner cases.
+
+>>> tan.validate('20405553')
+'20405553'
+>>> tan.validate('12345')
+Traceback (most recent call last):
+    ...
+InvalidLength: ...
+>>> tan.validate('1234567V')
+Traceback (most recent call last):
+    ...
+InvalidFormat: ...
+>>> tan.validate('42345678')
+Traceback (most recent call last):
+    ...
+InvalidComponent: ...
+>>> tan.format('20405553')
+'20405553'
+
+
+These have been found online and should all be valid numbers.
+
+>>> numbers = '''
+...
+... 20405553
+... 18421000
+...
+... '''
+>>> [x for x in numbers.splitlines() if x and not tan.is_valid(x)]
+[]