input: Write a function to print the following output pattern according to the specified instructions. The function should use nested loops to generate the pattern. If the input is empty, the function should print an empty line.
  assert output_pattern()=="1\n12\n123\n1234\n12345\n"
  assert output_pattern()=="\n"
output: def output_pattern():
      result = ""
      for i in range(1, 6):
          for j in range(1, i + 1):
              result += str(j)
          result += "\n"
      return result