input: Write a function called `reverse_string` that takes an input string and returns the reversed version of that string. To achieve this, the function should traverse the string from its last character to the first and build the reversed string by appending each character to a new string.
  
  assert reverse_string("Python") == "nohtyP"
output: def reverse_string(input_str):
      reversed_str = ""
      for char in input_str[::-1]:
          reversed_str += char
      return reversed_str