<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def wr_row_mergeall(self, worksheet, txtstr, fmt, row_idx):
 """Merge all columns and place text string in widened cell."""

        hdridxval = len(self.hdrs) - 1
        worksheet.merge_range(row_idx, 0, row_idx, hdridxval, txtstr, fmt)
        return row_idx + 1