ListView.py

ListView.py

class ListView():
  def __init__(self, items, slice_=None):
    start = (slice_.start if slice_ else None) or 0
    stop = (slice_.stop if slice_ else None) or float('inf')
    step = (slice_.step if slice_ else None) or 1
    if isinstance(items, ListView):
      self._items = items._items
      self._start = max(items._start, items._start + start)
      self._stop = min(items._stop, items._start + stop)
      self._step = items._step * step
    else:
      self._items = items
      self._start = start
      self._stop = stop
      self._step = step
    
  def __getitem__(self, key):
    if isinstance(key, slice):
      return ListView(self, key)
    return self._items[self._start + key * self._step]
  
  def __iter__(self):
    return (self._items[i] for i in range(self._start or 0, len(self._items) if self._stop == float('inf') else self._stop, self._step))

  def __len__(self):
    return (min(len(self._items), self._stop) - self._start) // self._step

One thing we could do to make this more flexible is not use len and indexing in __iter__. Instead we could iterate and skip _step items. We'd have to keep around some sort of pointer to the first item to start iterating over. That would allow us to slice into things like generators!

For the future: just adding where this script is referenced on StackOverflow

thank you!