input: Write a function to generate the following output pattern:
  
  1
  12
  123
  1234
  12345
  
  The function should take no input parameters and should print the pattern directly.
  
  assert print_pattern()==None
  assert print_pattern()==None
output: def print_pattern():
      for i in range(1, 6):
          for j in range(1, i + 1):
              print(j, end='')
          print()