86 lines
2.7 KiB
Python
86 lines
2.7 KiB
Python
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# imo.py - functions for handling IMO numbers
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# coding: utf-8
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#
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# Copyright (C) 2015 Arthur de Jong
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#
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# This library is free software; you can redistribute it and/or
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# modify it under the terms of the GNU Lesser General Public
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# License as published by the Free Software Foundation; either
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# version 2.1 of the License, or (at your option) any later version.
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#
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# This library is distributed in the hope that it will be useful,
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# but WITHOUT ANY WARRANTY; without even the implied warranty of
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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# Lesser General Public License for more details.
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#
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# You should have received a copy of the GNU Lesser General Public
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# License along with this library; if not, write to the Free Software
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# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
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# 02110-1301 USA
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"""IMO number (International Maritime Organization number).
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A number used to uniquely identify ships (the hull) for purposes of
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registering owners and management companies. The ship identification number
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consists of a six-digit sequentially assigned number and a check digit. The
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number is usually prefixed with "IMO".
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Note that there seem to be a large number of ships with an IMO that does not
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have a valid check digit or even have a different length.
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>>> validate('IMO 9319466')
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'9319466'
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>>> validate('IMO 8814275')
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'8814275'
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>>> validate('8814274')
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Traceback (most recent call last):
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...
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InvalidChecksum: ...
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>>> format('8814275')
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'IMO 8814275'
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"""
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from stdnum.exceptions import *
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from stdnum.util import clean
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def compact(number):
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"""Convert the number to the minimal representation. This strips the
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number of any valid separators and removes surrounding whitespace."""
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number = clean(number, ' ').upper().strip()
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if number.startswith('IMO'):
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number = number[3:]
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return number
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def calc_check_digit(number):
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"""Calculate the check digits for the number."""
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return str(sum(int(n) * (7 - i) for i, n in enumerate(number[:6])) % 10)
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def validate(number):
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"""Checks to see if the number provided is valid. This checks the length
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and check digit."""
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number = compact(number)
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if not number.isdigit():
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raise InvalidFormat()
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if len(number) != 7:
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raise InvalidLength()
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if calc_check_digit(number[:-1]) != number[-1]:
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raise InvalidChecksum()
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return number
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def is_valid(number):
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"""Checks to see if the number provided is valid. This checks the length
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and check digit."""
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try:
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return bool(validate(number))
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except ValidationError:
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return False
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def format(number):
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"""Reformat the passed number to the standard format."""
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return 'IMO ' + compact(number)
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