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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def visan(name=None):
 """ Creates the grammar for a V-ISAN code. This is a variation on the ISAN (International Standard Audiovisual Number) :param name: name for the field :return: grammar for an ISRC field """


    if name is None:
        name = 'V-ISAN Field'

    field = pp.Regex('[0-9]{25}')

    field.setName(name)

    return field.setResultsName('visan')