[Dave Hansen] > It seems when an item is 'remove'd from data, the rest of the list > 'shifts' over one, so what was 'next' now occupies the slot of the > 'remove'd item. When the next 'item' is selected from 'data', the > _desired_ 'next' item is skipped. So when 'data' has several > consecutive items to be deleted, only every other one is 'remove'd.
Your analysis is dead-on. Instead of being the "desired" item, the iterator fetches a[0], a[1], a[2], ... as determined by the state of the list when the index is retrieved. > Again, iterating over an item that is mutating seems like a Bad > Idea(tm) to me. Right. > But I was curious: is this the intended behavior, or > does this fall under what C programmers would call 'undefined > behavior.' It is intended. The behavior is defined as above (a series of indexed lookups). BTW, the usual ways to deal with this are to: 1. iterating from the right using: for item in reversed(data) 2. making a copy of the original list before iterating 3. creating a new result list: data = [x for x in data if 'DEL' not in x] Raymond -- http://mail.python.org/mailman/listinfo/python-list
