On 2007-12-10, Duncan Booth <[EMAIL PROTECTED]> wrote: > Neil Cerutti <[EMAIL PROTECTED]> wrote: >> Python's iterators are unsuitable for mutating the linked list >> while iterating--the only major application of linked lists. >> Wrapping in a generator won't allow you to use for loop >> syntax, unless I'm missing something, which has often >> happened. > > It is certainly possible to have a linked list implementation > which supports mutation while iterating. Here's a simple > example: > > import random > > class LinkedElement(object): > def __init__(self, value, next): > self.value = value > self.next = next > > class LinkedList(object): > def __init__(self, aList): > nxt = None > for el in reversed(aList): > nxt = LinkedElement(el, nxt) > self._cursor = self._list = LinkedElement(None, nxt) > > > def delete(self, element): > assert self._cursor.next is element > self._cursor.next = self._cursor.next.next > > def __iter__(self): > self._cursor = el = self._list > while el.next: > nxt = el.next > yield nxt > if nxt is el.next: > self._cursor = el = nxt > > def test(): > ll = LinkedList([random.randint(1,1000) for i in range(10)]) > > for el in ll: > if el.value%2==0: > ll.delete(el) > > print [el.value for el in ll] > > > if __name__=='__main__': > test() > > Support for deleting elements other than the current one, and > insertBefore/insertAfter methods is left as an exercise.
Making an object its own iterator for files, but not for a container. After the deletions, you can never iterate again. -- Neil Cerutti -- http://mail.python.org/mailman/listinfo/python-list
