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copied!<p>Here is some list functions based on <a href="https://stackoverflow.com/questions/280243/python-linked-list#280284">Martin v. Löwis's representation</a>:</p> <pre><code>cons = lambda el, lst: (el, lst) mklist = lambda *args: reduce(lambda lst, el: cons(el, lst), reversed(args), None) car = lambda lst: lst[0] if lst else lst cdr = lambda lst: lst[1] if lst else lst nth = lambda n, lst: nth(n-1, cdr(lst)) if n > 0 else car(lst) length = lambda lst, count=0: length(cdr(lst), count+1) if lst else count begin = lambda *args: args[-1] display = lambda lst: begin(w("%s " % car(lst)), display(cdr(lst))) if lst else w("nil\n") </code></pre> <p>where <code>w = sys.stdout.write</code></p> <p>Although doubly linked lists are famously used in Raymond Hettinger's <a href="http://code.activestate.com/recipes/576694-orderedset/" rel="noreferrer">ordered set recipe</a>, singly linked lists have no practical value in Python.</p> <p>I've <em>never</em> used a singly linked list in Python for any problem except educational. </p> <p>Thomas Watnedal <a href="https://stackoverflow.com/questions/280243/python-linked-list#280280">suggested</a> a good educational resource <a href="http://greenteapress.com/thinkpython/html/chap17.html" rel="noreferrer">How to Think Like a Computer Scientist, Chapter 17: Linked lists</a>:</p> <p>A linked list is either: </p> <ul> <li>the empty list, represented by None, or </li> <li><p>a node that contains a cargo object and a reference to a linked list.</p> <pre><code>class Node: def __init__(self, cargo=None, next=None): self.car = cargo self.cdr = next def __str__(self): return str(self.car) def display(lst): if lst: w("%s " % lst) display(lst.cdr) else: w("nil\n") </code></pre></li> </ul>

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