Pythonic equivalent of unshift or redo?

Question

I'm learning Python, and I have a situation where I want to consume items from an iterator. The tricky part is that under certain conditions, I want to "un-iterate." That is, put an item back onto the front of the iterator before I loop.

For example, suppose I'm picking apples from a tree. My fruit basket can only hold 10kg before it needs to be emptied. But I have to pick each apple before I can weigh it and determine if this apple would exceed the capacity of the basket.

In a language like Perl, I could unshift() the apple back onto the tree, and then let the loop expression re-pick the apple:

while ($apple = shift(@tree)) {
  $wt = weight($apple);
  if ($wt + weight(@basket) > 10) {
    send(@basket);
    @basket = ();
    unshift(@tree, $apple);
  } else {
    push(@basket, $element);
  }
}

Or else I can also use redo, which resumes processing at the top of block, without evaluating the loop expression. So the same apple can be re-processed, after the basket has been emptied.

while ($apple = shift(@tree)) {
  $wt = weight($apple);
  if ($wt + weight(@basket) > 10) {
    send(@basket);
    @basket = ();
    redo;
  } else {
    push(@basket, $apple);
  }
}

What would be the most pythonic solution for this kind of problem?

Answer 1

Why bother with unshifting when the else clause should always occur?

for apple in tree:
    if (apple.weight + basket.weight) > 10:
       send(basket)
       basket.clear()
    basket.add(apple)

Anyway, I'm fairly certain that Python doesn't have the sort of behavior you're looking for.