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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 rowstack(self, new, mode='nulls'):
 """ Vertical stacking for tabarrays. Stack tabarray(s) in `new` below `self`. **See also** :func:`tabular.tabarray.tab_rowstack`, :func:`tabular.spreadsheet.rowstack` """

        if isinstance(new,list):
            return tab_rowstack([self] + new, mode)
        else:
            return tab_rowstack([self, new], mode)