[英]Python: recursion in Class declaration
我正在尝试在 Python 的类声明中实现递归函数。 但是,该函数似乎不接受参数。 如果我在 Class 之外声明一个递归函数,它就可以工作。
[一个while循环][1]也可以解决问题。 (请参阅“遍历值”。恕我直言,我已经在键盘上敲了敲头,足以允许发布 SO 帖子。
class Node:
def __init__(self, value):
self.data = value
self.next = None
def traverse(self, node):
print(node.data)
if (node.next == None):
return
else:
node.traverse(node.next)
>>> a = Node('a')
>>> b = Node('b')
>>> c = Node('c')
>>> a.next = b
>>> b.next = c
>>> Node.traverse(a)
Traceback (most recent call last):
File "<pyshell#62>", line 1, in <module>
Node.traverse(a)
TypeError: traverse() missing 1 required positional argument: 'node'
[1]: https://medium.com/@kojinoshiba/data-structures-in-python-series-1-linked-lists-d9f848537b4d
一个更典型的实现是。
节点代码
class Node:
def __init__(self, value):
self.data = value
self.next = None
def traverse(self): # instance method (no 2nd argument node)
if self: # check if node
print(self.data) # output data
if self.next: # check for next node
self.next.traverse() # recursive call to next node if any
测试
a = Node('a')
b = Node('b')
c = Node('c')
a.next = b
b.next = c
a.traverse() # Note: Node.traverse(a) also works
# This is because
# When you call an instance method (e.g. traverse) from an
# instance object (e.g. a), Python automatically passes
# that instance object as the first argument (in addition
# to any other arguments) to the function call
# Thus: a.traverse() becomes Node.traverse(a)
输出
a
b
c
您需要使traverse
成为类方法。 目前,它表示您缺少node
参数,因为在Node.traverse(a)
您提供了self=a
而不是node=a
。
class Node:
def __init__(self, value):
self.data = value
self.next = None
@classmethod # This is the only addition needed :)
def traverse(self, node):
print(node.data)
if node.next is None:
return
else:
node.traverse(node.next)
在Python Cookbook
,第 117 页,你会发现这个秘诀是这个问题的更好解决方案:
class Node:
def __init__(self, value):
self._value = value
self._children = []
def __repr__(self):
return 'Node({!r})'.format(self._value)
def add_child(self, node):
self._children.append(node)
def __iter__(self):
return iter(self._children)
def depth_first(self):
yield self
for c in self:
yield from c.depth_first()
if __name__ == '__main__':
root = Node(0)
child1 = Node(1)
child2 = Node(2)
root.add_child(child1)
root.add_child(child2)
child1.add_child(Node(3))
child1.add_child(Node(4))
child2.add_child(Node(5))
for ch in root.depth_first():
print(ch)
尝试使用这个。
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