2 files changed, 120 insertions, 0 deletions
diff --git a/stdnum/gt/__init__.py b/stdnum/gt/__init__.py
new file mode 100644
index 0000000..c1f38d9
--- /dev/null
+++ b/stdnum/gt/__init__.py
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+# __init__.py - collection of Guatemalan numbers
+# coding: utf-8
+#
+# Copyright (C) 2019 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
+
+"""Collection of Guatemalan numbers."""
+
+# provide aliases
+from stdnum.gt import nit as vat  # noqa: F401
diff --git a/stdnum/gt/nit.py b/stdnum/gt/nit.py
new file mode 100644
index 0000000..efbe1b0
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+++ b/stdnum/gt/nit.py
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+# nit.py - functions for handling Guatemala NIT numbers
+# coding: utf-8
+#
+# Copyright (C) 2019 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
+
+"""NIT (Número de Identificación Tributaria, Guatemala tax number).
+
+The Número de Identificación Tributaria (NIT) is an identifier of legal
+entities for tax purposes in Guatemala.
+
+The number consists of 2 to 12 characters, where the last one is the check
+digit (a digit or the letter K) and the rest are digits. Leading zeroes are
+usually omitted. Digits and check digit are usually separated with a hyphen.
+
+More information:
+
+* https://portal.sat.gob.gt/portal/descarga/6524/factura-electronica-fel/25542/fel-reglas-y-validaciones.pdf (page 58)
+* https://portal.sat.gob.gt/portal/consulta-cui-nit/
+
+>>> validate('576937-K')
+'576937K'
+>>> validate('7108-0')
+'71080'
+>>> validate('8977112-0')
+Traceback (most recent call last):
+    ...
+InvalidChecksum: ...
+>>> validate('1234567890123')
+Traceback (most recent call last):
+    ...
+InvalidLength: ...
+>>> format('39525503')
+'3952550-3'
+"""
+
+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, ' -').upper().strip().lstrip('0')
+
+
+def calc_check_digit(number):
+    """Calculate the check digit. The number passed should not have the
+    check digit included."""
+    c = -sum(i * int(n) for i, n in enumerate(reversed(number), 2)) % 11
+    return 'K' if c == 10 else str(c)
+
+
+def validate(number):
+    """Check if the number is a valid Guatemala NIT number.
+
+    This checks the length, formatting and check digit.
+    """
+    number = compact(number)
+    if len(number) < 2 or len(number) > 12:
+        raise InvalidLength()
+    if not isdigits(number[:-1]):
+        raise InvalidFormat()
+    if number[-1] != 'K' and not isdigits(number[-1]):
+        raise InvalidFormat()
+    if number[-1] != calc_check_digit(number[:-1]):
+        raise InvalidChecksum()
+    return number
+
+
+def is_valid(number):
+    """Check if the number is a valid Guatemala NIT number."""
+    try:
+        return bool(validate(number))
+    except ValidationError:
+        return False
+
+
+def format(number):
+    """Reformat the number to the standard presentation format."""
+    number = compact(number)
+    return '-'.join([number[:-1], number[-1]])