input: 
  def replace_all_occurrences(str: str, char: str, replacement: str) -> str:
      """ Replace all occurrences of the character 'char' in the string 'str' 
      with the provided 'replacement' character.
      >>> replace_all_occurrences("Hello World!", 'l', 'X')
      'HeXXo WorXd!'
      >>> replace_all_occurrences("Python Programming", 'o', '0')
      'Pyth0n Pr0gr0mming'
      """
  
output:     result = ""
      for c in str:
          if c == char:
              result += replacement
          else:
              result += c
      return result