Returns a worksheet with specified `index`.

        :param index: An index of a worksheet. Indexes start from zero.
        :type index: int

        :returns: an instance of :class:`gsperad.models.Worksheet`
                  or `None` if the worksheet is not found.

        Example. To get first worksheet of a spreadsheet:

        >>> sht = client.open('My fancy spreadsheet')
        >>> worksheet = sht.get_worksheet(0)

def get_worksheet(self, index):
        """Returns a worksheet with specified `index`.

        :param index: An index of a worksheet. Indexes start from zero.
        :type index: int

        :returns: an instance of :class:`gsperad.models.Worksheet`
                  or `None` if the worksheet is not found.

        Example. To get first worksheet of a spreadsheet:

        >>> sht = client.open('My fancy spreadsheet')
        >>> worksheet = sht.get_worksheet(0)

        """
        sheet_data = self.fetch_sheet_metadata()

        try:
            properties = sheet_data['sheets'][index]['properties']
            return Worksheet(self, properties)
        except (KeyError, IndexError):
            return None