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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 Open(self):
 """Creates a new workbook. Raises: IOError: if the specified output file already exists. OSError: if the specified output file already exists. ValueError: if the filename is not set. """

    if not self._filename:
      raise ValueError('Missing filename.')

    if os.path.isfile(self._filename):
      raise IOError((
          'Unable to use an already existing file for output '
          '[{0:s}]').format(self._filename))

    options = {
        'constant_memory': True,
        'strings_to_urls': False,
        'strings_to_formulas': False,
        'default_date_format': self._timestamp_format}
    self._workbook = xlsxwriter.Workbook(self._filename, options)
    self._sheet = self._workbook.add_worksheet('Sheet')
    self._current_row = 0