firstįirst dllistnode object in the list. This object represents a doubly linked list data structure. dllist and a singly linked data structure sllist. Llist module implements linked list data structures. """A singleton representing an empty list."""ĭef _nonzero_(self): return head(self): raise Inde圎rror("End of tail(self): raise Inde圎rror("End of list") Return "LinkedList()" % ', '.join(map(repr,self)) """Acts as cmp(): -1 for self b: return 1 No_copy_needed = (stop = length) and (step = 1)ĭef _le_(self, other): return self._cmp(other) = 0 Length = len(self) # Need to calc length. ![]() If (start >= 0) and (idx.stop is None) and (idx.step is None or idx.step = 1): # We can't do this for more complicated slices however (eg # Special case: Avoid constructing a new list, or performing O(n) length Start=l = LinkedList(iter(self)) # Create copy, as we'll mutate # head and tail are not head(self): return tail(self): return self._tail Return cls.EmptyList # Return empty list singleton. If isinstance(l, LinkedList): return l # Immutable, so no copy needed. # this should be transparent to the user. ![]() # non-contiguous range, we do need to create a copy. # For cases where the slice stops before the end, or uses a # Normal list indexing and slice operations can be performed. # Or prepending arbitrary sequences (Still no copy of l performed): # Prepending is O(1) and can be done with: It will have the desired big O performance characteristics however.Įxample of usage: > l = LinkedList() It won't be as space or time efficient as lisp cons cells, as python classes are obviously a bit more heavyweight (You could improve things slightly with " _slots_ = '_head','_tail'" to reduce memory usage). It should have O(1) prepend, doesn't copy data unless it needs to and can be used pretty interchangably with tuples. supports indexing, slicing, concatenation with arbitrary sequences etc). Here's a slightly more complex version of a linked list class, with a similar interface to python's sequence types (ie. Out = 'LinkedList [\n' str(current.value) '\n' class Node:ĭef _init_(self, value = None, next = None): It is a simple LinkedList class based on the straightforward C design and Chapter 17: Linked lists, as recommended by Thomas Watnedal. Here is a more standard design: L = LinkedList() The accepted answer is rather complicated. class Node:ĭef _init_(self, cargo=None, next=None): the empty list, represented by None, orĪ node that contains a cargo object and a reference to a linked list.Thomas Watnedal suggested a good educational resource How to Think Like a Computer Scientist, Chapter 17: Linked lists: I've never used a singly linked list in Python for any problem except educational. Length = lambda lst, count=0: length(cdr(lst), count 1) if lst else countĭisplay = lambda lst: begin(w("%s " % car(lst)), display(cdr(lst))) if lst else w("nil\n")Īlthough doubly linked lists are famously used in Raymond Hettinger's ordered set recipe, singly linked lists have no practical value in Python. Nth = lambda n, lst: nth(n-1, cdr(lst)) if n > 0 else car(lst) Mklist = lambda *args: reduce(lambda lst, el: cons(el, lst), reversed(args), None) ![]() Löwis's representation: cons = lambda el, lst: (el, lst) Here is some list functions based on Martin v.
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