old_contents: def fib1(amount):
      """
      Fibonacci generator example. The second variable is used to store
      the result.
      :param amount: Amount of numbers to produce.
      :return: Generator.
  
      >>> list(fib1(0))
      []
      >>> list(fib1(1))
      [0]
      >>> list(fib1(3))
      [0, 1, 1]
      >>> list(fib1(9))
      [0, 1, 1, 2, 3, 5, 8, 13, 21]
      """
      first, second = 0, 1
      for _ in range(amount):
          yield first
          first, second = second + first, first
  
  
  def fib2(amount):
      """
      Fibonacci generator example. The first variable is used to store
      the result.
      :param amount: Amount of numbers to produce.
      :return: Generator.
  
      >>> list(fib2(0))
      []
      >>> list(fib2(1))
      [0]
      >>> list(fib2(3))
      [0, 1, 1]
      >>> list(fib2(9))
      [0, 1, 1, 2, 3, 5, 8, 13, 21]
      """
      first, second = 1, 0
      for _ in range(amount):
          first, second = second, first + second
          yield first
  
  
  if __name__ == '__main__':
      import doctest
  
      doctest.testmod()
  
new_contents: """Implementations calculation of Fibonacci numbers."""
  
  
  def fib1(amount):
      """
      Calculate Fibonacci numbers.
  
      The second variable is used to store the result.
      :param amount: Amount of numbers to produce.
      :return: Generator.
  
      >>> list(fib1(0))
      []
      >>> list(fib1(1))
      [0]
      >>> list(fib1(3))
      [0, 1, 1]
      >>> list(fib1(9))
      [0, 1, 1, 2, 3, 5, 8, 13, 21]
      """
      first, second = 0, 1
      for _ in range(amount):
          yield first
          first, second = second + first, first
  
  
  def fib2(amount):
      """
      Calculate Fibonacci numbers.
  
      The first variable is used to store the result.
      :param amount: Amount of numbers to produce.
      :return: Generator.
  
      >>> list(fib2(0))
      []
      >>> list(fib2(1))
      [0]
      >>> list(fib2(3))
      [0, 1, 1]
      >>> list(fib2(9))
      [0, 1, 1, 2, 3, 5, 8, 13, 21]
      """
      first, second = 1, 0
      for _ in range(amount):
          first, second = second, first + second
          yield first
  
  
  if __name__ == '__main__':
      import doctest
  
      doctest.testmod()
  
subject: Adjust doc strings in Fibonacci numbers implementation