#! /usr/bin/env python
#
def isbn_is_valid ( s ):

#*****************************************************************************80
#
## ISBN_IS_VALID reports whether an ISBN is valid.
#
#  Discussion:
#
#    ISBN stands for International Standard Book Number.  A unique ISBN
#    is assigned to each new book.  The ISBN includes 10 digits.  There is
#    an initial digit, then a dash, then a set of digits which are a
#    code for the publisher, another digit, and then the check digit:
#
#      initial-publisher-book-check
#
#    The number of digits used for the publisher and book codes can vary,
#    but the check digit is always one digit, and the total number of
#    digits is always 10.
#
#    The check digit is interesting, because it is a way of trying to
#    make sure that an ISBN has not been incorrectly copied.  Specifically,
#    if the ISBN is correct, then its ten digits will satisfy
#
#       10 * A + 9 * B + 8 * C + 7 * D + 6 * E
#      + 5 * F * 4 * G * 3 * H + 2 * I +     J  = 0 mod 11.
#
#    Here, we've taken 'A' to represent the first digit and 'J' the
#    last (which is the check digit).  In order for the code to work,
#    the value of J must be allowed to be anything from 0 to 10.  In
#    cases where J works out to be 10, the special digit 'X' is used.
#    An 'X' digit can only occur in this last check-digit position
#    on an ISBN.
#
#  Licensing:
#
#    This code is distributed under the GNU LGPL license. 
#
#  Modified:
#
#    17 September 2015
#
#  Author:
#
#    John Burkardt
#
#  Parameters:
#
#    Input, string S, a string containing 12 digits.
#    Dashes and other characters will be ignored.
#
#    Output, bool VALUE, is TRUE if the string is valid.
#
  from isbn_check_digit_calculate import isbn_check_digit_calculate
  from isbn_digit_to_i4 import isbn_digit_to_i4
  from s_to_isbn_digits import s_to_isbn_digits

  n = 10
  dvec = s_to_isbn_digits ( s, n )

  c1 = isbn_check_digit_calculate ( s )
  d1 = isbn_digit_to_i4 ( c1 )

  d2 = dvec[9]

  if ( d1 == d2 ):
    value = True
  else:
    value = False

  return value

def isbn_is_valid_test ( ):

#*****************************************************************************80
#
## ISBN_IS_VALID_TEST tests ISBN_IS_VALID.
#
#  Licensing:
#
#    This code is distributed under the GNU LGPL license.
#
#  Modified:
#
#    17 September 2015
#
#  Author:
#
#    John Burkardt
#
  import platform

  print ( '' )
  print ( 'ISBN_IS_VALID_TEST' )
  print ( '  Python version: %s' % ( platform.python_version ( ) ) )
  print ( '  ISBN_IS_VALID reports whether a ISBN is valid.' )
  print ( '' )
#
#  Supply a valid code, with dashes.
#
  s1 = '0-306-40615-2'
  value1 = True
  value2 = isbn_is_valid ( s1 )
  print ( '  Validity of "%s" is %s, expecting %s' % ( s1, value2, value1 ) )
#
#  Modify one digit.
#
  s1 = '0-326-40615-2'
  value1 = False
  value2 = isbn_is_valid ( s1 )
  print ( '  Validity of "%s" is %s, expecting %s' % ( s1, value2, value1 ) )
#
#  Supply a valid code, with spaces.
#
  s1 = '0 8493 9640 9';
  value1 = True
  value2 = isbn_is_valid ( s1 )
  print ( '  Validity of "%s" is %s, expecting %s' % ( s1, value2, value1 ) )
#
#  Modify the check digit.
#
  s1 = '0 8493 9640 3'
  value1 = False
  value2 = isbn_is_valid ( s1 )
  print ( '  Validity of "%s" is %s, expecting %s' % ( s1, value2, value1 ) )
#
#  Supply a valid code, with final digit 'X'.
#
  s1 = '0-3870-9654-X'
  value1 = True
  value2 = isbn_is_valid ( s1 )
  print ( '  Validity of "%s" is %s, expecting %s' % ( s1, value2, value1 ) )
#
#  Supply a valid code, with final digit 'x'.
#
  s1 = '0-201-38597-x'
  value1 = True
  value2 = isbn_is_valid ( s1 )
  print ( '  Validity of "%s" is %s, expecting %s' % ( s1, value2, value1 ) )
#
#  Terminate.
#
  print ( '' )
  print ( 'ISBN_IS_VALID_TEST:' )
  print ( '  Normal end of execution.' )
  return

if ( __name__ == '__main__' ):
  from timestamp import timestamp
  timestamp ( )
  isbn_is_valid_test ( )
  timestamp ( )