'Replace string values in col.str_vals'

def _replace_vals(self, cols):

    if self.fill_values:
        for col in (col for col in cols if col.fill_values):
            for (i, str_val) in ((i, x) for (i, x) in enumerate(col.str_vals) if (x in col.fill_values)):
                col.str_vals[i] = col.fill_values[str_val]
            if ((masked in col.fill_values) and hasattr(col, 'mask')):
                mask_val = col.fill_values[masked]
                for i in col.mask.nonzero()[0]:
                    col.str_vals[i] = mask_val
