Print string and data structures used Pascal's Triangle

Print Pascal's Triangle

def main():
 num = int(input('Number of rows: '))
 yh = [[]] * num
 for row in range(len(yh)):
   yh[row] = [None] * (row + 1)
   for col in range(len(yh[row])):
     if col == 0 or col == row:
       yh[row][col] = 1
     else:
       yh[row][col] = yh[row - 1][col] + yh[row - 1][col - 1] 
     print(yh[row][col], end='\t')
   print('\n')
     
 print()

if __name__ == '__main__':
 main()