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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 col_values(self, col, value_render_option='FORMATTED_VALUE'):
 """Returns a list of all values in column `col`. Empty cells in this list will be rendered as :const:`None`. :param col: Column number. :type col: int :param value_render_option: (optional) Determines how values should be rendered in the the output. See `ValueRenderOption`_ in the Sheets API. :type value_render_option: str .. _ValueRenderOption: https://developers.google.com/sheets/api/reference/rest/v4/ValueRenderOption """


        start_label = rowcol_to_a1(1, col)
        range_label = '%s!%s:%s' % (self.title, start_label, start_label[:-1])

        data = self.spreadsheet.values_get(
            range_label,
            params={
                'valueRenderOption': value_render_option,
                'majorDimension': 'COLUMNS'
            }
        )

        try:
            return data['values'][0]
        except KeyError:
            return []