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PORecursion Depth Exceeded - Python Doubly-Linked List
 

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  1. PORecursion Depth Exceeded - Python Doubly-Linked List
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    <p>I'm in the process of creating a FIFO implemented as a doubly-linked list, but I'm at a loss as to why I'm receiving a recursion error. I've posted my code and the error I received below. Any help would be much appreciated! </p> <pre><code>"""DLList.py""" class DLList(object): """A doubly-linked list attributes: nl = node list""" def __init__(self, nl=[]): self.nl = nl def __str__(self): return str(self.nl) def __len__(self): return len(self.nl) def append(self, node): if not isinstance(node, DLNode): raise TypeError try: node.pn = self.nl[-1] node.pn.nn = node self.nl.append(node) except: self.nl.append(node) def pop(self): rn = self.nl.pop(0) try: self.nl[0].pn = None except: pass return rn class DLNode(object): """A node in a doubly-linked list. attributes: self.pn = previous node, self.data = data, self.nn = next node""" def __init__(self, data): self.pn = None self.data = data self.nn = None def __str__(self): return '[%s, %s, %s]' % (self.pn, self.data, self.nn) a = DLNode(17) b = DLNode(15) c = DLNode(12) d = DLNode(46) e = DLNode(46) ages = DLList() ages.append(a) ages.append(b) ages.append(c) ages.append(d) ages.append(e) print ages.pop() </code></pre> <p>I received this error:</p> <pre><code>File "C:\python\swampy-2.0\DLList.py", line 43, in __str__ return '[%s, %s, %s]' % (self.pn, self.data, self.nn) RuntimeError: maximum recursion depth exceeded </code></pre> <p>The thing is, I never intended to use recursion, and I can't figure out why I've entered into a recursive loop. ages.pop() is meant to return an instance of DLNode.</p>
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    1. USMadison May
    1. USMadison May
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      1. VTUpMod
    1. COOne thing, don't use `[]` as your default argument. Every instance of `DLList` will reference the same `list` instance in this case. Use `None` and then check for `None` and generate a new `list` object on the fly in `__init__`.
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      1. PORecursion Depth Exceeded - Python Doubly-Linked List
      1. USSilas Ray
    2. COValid point. Thanks!
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      1. USMadison May
 

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