input: Write a function to determine if it is possible to represent a given string in the format of a complex number. If it is possible return True else return False. If the given string is empty then return True.
  
  assert is_complex_number("3+4i")==True
  assert is_complex_number("5j")==True
  assert is_complex_number("3-4i")=True
  assert is_complex_number("2.5+6.7i")==True
  assert is_complex_number("3.14")==False
  assert is_complex_number("i")==False
  assert is_complex_number("")==True
output: def is_complex_number(s):
      if s == "":
          return True
      try:
          complex(s)
          return True
      except ValueError:
          return False