input: def find_extreme_integers(lst):
      '''
      Develop a function that returns a tuple (x, y), where 'x' is
      the largest negative integer, and 'y' is the smallest
      positive integer within a given list.
      If there are no negative or positive integers, return None for those values.
  
      Examples:
      find_extreme_integers([2, 4, 1, 3, 5, 7]) == (None, 1)
      find_extreme_integers([]) == (None, None)
      find_extreme_integers([0]) == (None, None)
      '''
output:     negative_numbers = [num for num in lst if num < 0]
      positive_numbers = [num for num in lst if num > 0]
  
      if negative_numbers:
          x = max(negative_numbers)
      else:
          x = None
  
      if positive_numbers:
          y = min(positive_numbers)
      else:
          y = None
  
      return (x, y)