本文详细介绍了如何构建和拓展Python的链表类，包括初始化节点、节点合并、遍历、长度计算、比较运算符重载、属性装饰器、节点链创建方法以及算术运算符重载。通过实例展示了如何创建有序链表、合并链表、添加节点、判断链表相等性等操作，进一步了解Python面向对象编程的灵活性。
前提知识点
本文以准备以“链表类”为例，一步步深入了解学习“类”的各种功能实现。关于链表的概念定义略，详见上一篇文章的介绍： 链接地址点这里快速到达
一个最基础的节点类
就一个初始化方法 __init__()，定义一个节点类
三个属性： 其中，val和value是等价的，表示节点存储的数据； next 表示指针，指向下一节点。
class Node():
def __init__(self, value=None, Next=None):
self.val = self.value = value
self.next = Next
'''
# 测试：
>>> node = Node(1)
>>> node.next = Node(2)
>>> node.val
1
>>> node.value
1
>>> node.next.val
2
>>>
>>> node = Node(1, Node(2))
>>> node.val
1
>>> node.next.value
2
>>>
'''
进一步尝试其他操作：
>>> node = Node()
>>> help(Node)
Help on class Node in module __main__:
class Node(builtins.object)
| Node(value=None, Next=None)
|
| Methods defined here:
|
| __init__(self, value=None, Next=None)
| Initialize self. See help(type(self)) for accurate signature.
|
| ----------------------------------------------------------------------
| Data descriptors defined here:
|
| __dict__
| dictionary for instance variables (if defined)
|
| __weakref__
| list of weak references to the object (if defined)
>>> node
<__main__.Node object at 0x00375B68>
>>> node.__doc__
>>> node.__dict__
{'val': None, 'value': None, 'next': None}
>>> node = Node(1,Node(2))
>>> node.__dict__
{'val': 1, 'value': 1, 'next': <__main__.Node object at 0x00375BB0>}
类的方法定义、数据描述符定义等就一两项，说明文档也为空。但就这么简单的类，已经可以用它解决实际问题了，来举个简单的例子：
将两个有序链表(升序)合并为一个新的有序链表并返回。
List1: 1->2>4->8 List2: 1->3->3->5->5
把可以反复利用的代码，新写两个函数拓展到这个类里：除了主要功能合并方法外，另写一个便于检查是否正确的遍历方法。
拓展一： 新增方法
>>> class Node():
def __init__(self, value=None, Next=None):
self.val = self.value = value
self.next = Next
def merge(self, node):
ret = cur = Node()
while self is not None and node is not None:
if self.val < node.val:
cur.next = self
self = self.next
else:
cur.next = node
node = node.next
cur = cur.next
cur.next = self or node
return ret.next
def travel(self):
ret,cur = [],self
while cur is not None:
ret.append(cur.val)
cur = cur.next
return ret
测试结果：
>>> NodeList1 = Node(1,Node(2,Node(4,Node(8))))
>>> NodeList2 = Node(1,Node(3,Node(3,Node(5,Node(5)))))
>>> NodeList1.travel()
[1, 2, 4, 8]
>>> NodeList2.travel()
[1, 3, 3, 5, 5]
>>> NodeList = NodeList1.merge(NodeList2)
>>> NodeList.travel()
[1, 1, 2, 3, 3, 4, 5, 5, 8]
>>>
经测试，完全正确！
拓展二：魔法方法
先看一下，自定义节点类与内置list列表类的对比结果：
>>> l = list([1,2,3])
>>> len(l)
3
>>> str(l)
'[1, 2, 3]'
>>> l
[1, 2, 3]
>>> type(l)
<class 'list'>
>>> type(l) is list
True
>>>
>>> n = Node(1,Node(2,Node(3)))
>>> len(n)
Traceback (most recent call last):
File "<pyshell#82>", line 1, in <module>
len(n)
TypeError: object of type 'Node' has no len()
>>> str(n)
'<__main__.Node object at 0x0000000002CD28B0>'
>>> n
'<__main__.Node object at 0x0000000002CD28B0>'
>>> type(n)
<class '__main__.Node'>
>>> type(n) is Node
True
>>> 肯定败下阵来，看来需要请出__len__, __str__, __repr__等这些标准的类内置方法（命名两头均是双下划线，是类内置的内部方法，这种特殊方法也被称为“魔法方法”），来模拟一下内置类可以被len(), 被str()的功能。同时去掉merge方法，travel改名为values，重写原travel，最后新增全局变量__doc__，__version__，__all__等用于返回信息。
class Node():
'''class Node of Singlelinked List'''
__version__ = '1.0.0'
__all__ = ['size','travel','values','__version__']
def __init__(self, value=None, Next=None):
self.val = self.value = value
self.next = Next
def __repr__(self):
return f'Node({self.val}->{self.next})'
def __str__(self):
return f'{self.val}->{self.next}'
def __len__(self):
if self.val is None:
return 0
size,cur = 0,self
while cur is not None:
size += 1
cur = cur.next
return size
def __add__(self, other):
if self.val is None:
self = other
return self
cur = self
while cur.next is not None:
cur = cur.next
cur.next = other
self.next = cur
return self
def values(self):
ret,cur = [],self
while cur is not None:
ret.append(cur.val)
cur = cur.next
return ret
def travel(self):
ret = self.__str__()
return ret[:-6]
def size(self):
return self.__len__()测试结果：
>>> n = Node(1,Node(2,Node(3)))
>>> n.__all__
['size', 'travel', 'values', '__version__']
>>> n.__doc__
'class Node of Singlelinked List'
>>> n.__version__
'1.0.0'
>>> n.__dict__
{'val': 1, 'value': 1, 'next': Node(2->3->None)}
>>> n.size()
3
>>> len(n)
3
>>> n.__len__() # 就是用来被len()调用的，一般情况不会使用内部方法
3
>>> str(n)
'1->2->3->None'
>>> n.__str__() # 就是用来被str()调用的，一般情况不会使用内部方法
'1->2->3->None'
>>> repr(n)
'Node(1->2->3->None)'
>>> n.__repr__() # 就是用来被repr()调用的，一般情况不会使用内部方法
'Node(1->2->3->None)'
>>> n # 变量本身也是repr的结果，但输出时没有引号
Node(1->2->3->None)
>>> n.travel()
'1->2->3'
>>> n.values()
[1, 2, 3]
>>>
是不是很赞？ 魔法方法不仅仅只有这几个基本的，它共有八大类好几十种呢。它的本质就是用来实现重载对象的方法，可以用于重载算术运算、逻辑比较、类型转换、容器迭代等。
注：这个类里的__repr__、__str__是以递归实现的，与python允许的最大值递归深度有关，大概340个元素以上的会报错。但 .values .travel用遍历得来，不受影响。
拓展三：重载比较运算符
以比较运算（＞、＜、==）为例，先看一下未重载之前的效果：
>>> a,b=Node(1,Node(2,Node(3))),Node(1,Node(2,Node(3)))
>>> a==b
False
>>> a>b
Traceback (most recent call last):
File "<pyshell#123>", line 1, in <module>
a>b
TypeError: '>' not supported between instances of 'Node' and 'Node'
>>> a<b
Traceback (most recent call last):
File "<pyshell#124>", line 1, in <module>
a<b
TypeError: '<' not supported between instances of 'Node' and 'Node'
>>> 结果：大于或小于没法用，等于么即便是两条节点链(多个节点相接而成)的所有节点都一一相等也返回False。
重载时比较运算（＞、＜、==）分别对应（__gt__、__lt__、__nq__），各是： greater than, less than, equal to 的意思。重载约定，两个节点链哪个节点数多就哪个大，节点数一样时每个节点值都相等为“==全等”，代码如下：
class Node():
'''class Node of Singlelinked List'''
__version__ = '1.0.0'
__all__ = ['size','travel','values','__version__']
def __init__(self, value=None, Next=None):
self.val = self.value = value
self.next = Next
def __repr__(self):
return f'Node({self.val}->{self.next})'
def __str__(self):
return f'{self.val}->{self.next}'
def __len__(self):
if self.val is None:
return 0
size,cur = 0,self
while cur is not None:
size += 1
cur = cur.next
return size
def __gt__(self, other):
if len(self)>len(other):
return True
else:
return False
def __lt__(self, other):
if len(self)<len(other):
return True
else:
return False
def __eq__(self, other):
cur1,cur2 = self,other
if len(cur1)!=len(cur2):
return False
while cur1 is not None:
if cur1.val!=cur2.val:
return False
cur1 = cur1.next
cur2 = cur2.next
else:
return True
def values(self):
ret,cur = [],self
while cur is not None:
ret.append(cur.val)
cur = cur.next
return ret
def travel(self):
ret = self.__str__()
return ret[:-6]
def size(self):
return self.__len__()测试效果：
>>> a,b = Node(1,Node(2,Node(3))), Node(1,Node(2,Node(3)))
>>> a == b
True
>>> a > b
False
>>> a < b
False
>>>
>>> a,b = Node(1,Node(2,Node(3))), Node(3,Node(2))
>>> a > b
True
>>> a < b
False
>>> a == b
False
>>> b > a
False
>>> b < a
True
>>>
已完美达到预期效果！
拓展四：属性装饰器
用类属性装饰器@property标注类方法，能使类的方法变为只读属性。以下代码把values()方法和另一个与size()方法相同功能的length()方法转变成两个属性： values和length：
class Node():
'''class Node of Singlelinked List'''
__version__ = '1.0.0'
__all__ = ['length','value','values','cat','size','travel','__version__']
def __init__(self, value=None, Next=None):
self.val = self.value = value
self.next = Next
def __repr__(self):
return f'Node({self.val}->{self.next})'
def __str__(self):
return f'{self.val}->{self.next}'
def __len__(self):
if self.val is None:
return 0
size,cur = 0,self
while cur is not None:
size += 1
cur = cur.next
return size
def __gt__(self, other):
if len(self)>len(other):
return True
else:
return False
def __lt__(self, other):
if len(self)<len(other):
return True
else:
return False
def __eq__(self, other):
cur1,cur2 = self,other
if len(cur1)!=len(cur2):
return False
while cur1 is not None:
if cur1.val!=cur2.val:
return False
cur1 = cur1.next
cur2 = cur2.next
else:
return True
@property
def values(self):
ret,cur = [],self
while cur is not None:
ret.append(cur.val)
cur = cur.next
return ret
def travel(self):
ret = self.__str__()
return ret[:-6]
def size(self):
return self.__len__()
@property
def length(self):
return self.__len__()测试结果：
>>> a,b = Node(1,Node(2,Node(3))),Node(4,Node(5))
>>> a.length
3
>>> a.values
[1, 2, 3]
>>> b.length
2
>>> b.values
[4, 5]
>>
>>> b.next.next = a
>>> b
Node(4->5->1->2->3->None)
>>> b.length
5
>>> b.values
[4, 5, 1, 2, 3]
>>>
一个节点类的代码基本成型了，此时类的帮助返回如下：
>>> help(Node)
Help on class Node in module __main__:class Node(builtins.object)
| Node(value=None, Next=None)
|
| class Node of Singlelinked List
|
| Methods defined here:
|
| __eq__(self, other)
| Return self==value.
|
| __gt__(self, other)
| Return self>value.
|
| __init__(self, value=None, Next=None)
| Initialize self. See help(type(self)) for accurate signature.
|
| __len__(self)
|
| __lt__(self, other)
| Return self<value.
|
| __repr__(self)
| Return repr(self).
|
| __str__(self)
| Return str(self).
|
| size(self)
|
| travel(self)
|
| ----------------------------------------------------------------------
| Readonly properties defined here:
|
| length
|
| values
|
| ----------------------------------------------------------------------
| Data descriptors defined here:
|
| __dict__
| dictionary for instance variables (if defined)
|
| __weakref__
| list of weak references to the object (if defined)
|
| ----------------------------------------------------------------------
| Data and other attributes defined here:
|
| __all__ = ['length', 'value', 'values', 'size', 'travel', '__version__...
|
| __hash__ = None>>>
>>> Node.__all__
['length', 'value', 'values', 'size', 'travel', '__version__']
>>> dir(Node)
['__add__', '__all__', '__class__', '__delattr__', '__dict__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__gt__', '__hash__', '__init__', '__init_subclass__', '__le__', '__len__', '__lt__', '__module__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__', '__version__', '__weakref__', 'cat', 'length', 'size', 'travel', 'values']
>>>
拓展五：创建节点链方法
增加新增、追加、创建等方法，方便节点的赋值，没有设置这些方法时赋值也要写代码，如：
>>> n = Node(1)
>>> t = n
>>> for i in range(2,10):
t.next = Node(i)
t = t.next
print(n)
1->2->None
1->2->3->None
1->2->3->4->None
1->2->3->4->5->None
1->2->3->4->5->6->None
1->2->3->4->5->6->7->None
1->2->3->4->5->6->7->8->None
1->2->3->4->5->6->7->8->9->None
>>>
>>>
>>> n = Node(9)
>>> for i in reversed(range(1,9)):
n = Node(i, n)
print(n)
8->9->None
7->8->9->None
6->7->8->9->None
5->6->7->8->9->None
4->5->6->7->8->9->None
3->4->5->6->7->8->9->None
2->3->4->5->6->7->8->9->None
1->2->3->4->5->6->7->8->9->None有了以上经验，添加push,append,cat三个方法和一个函数build()，代码如下：
class Node():
'''class Node of Singlelinked List'''
__version__ = '1.0.1'
__all__ = ['length','value','values',
'push','append','cat', 'build',
'size','travel','__version__']
def __init__(self, value=None, Next=None):
self.val = self.value = value
self.next = Next
def __repr__(self):
return f'Node({self.val}->{self.next})'
def __str__(self):
return f'{self.val}->{self.next}'
def __len__(self):
if self.val is None:
return 0
size,cur = 0,self
while cur is not None:
size += 1
cur = cur.next
return size
def __gt__(self, other):
if len(self)>len(other):
return True
else:
return False
def __lt__(self, other):
if len(self)<len(other):
return True
else:
return False
def __eq__(self, other):
cur1,cur2 = self,other
if type(cur1) is not Node:
return False
if type(cur2) is not Node:
return False
if len(cur1)!=len(cur2):
return False
while cur1 is not None:
if cur1.val!=cur2.val:
return False
cur1 = cur1.next
cur2 = cur2.next
else:
return True
@property
def values(self):
ret,cur = [],self
while cur:
ret.append(cur.val)
cur = cur.next
return ret
def travel(self):
ret = self.__str__()
return ret[:-6]
def size(self):
return self.__len__()
@property
def length(self):
return self.__len__()
def append(self, value):
'''在尾节点后追加数据或节点，数据允许为可迭代对象'''
if self.val is None:
self = Node.build(value)
return self
node = self
while node.next:
node = node.next
if type(value) is Node:
node.next = value
else:
tmp = Node.build(value)
node.next = tmp
return self
def push(self, value):
'''在头节点前插入数据或节点，数据允许为可迭代对象'''
tmp = Node(self.val,self.next)
if type(value) is Node:
ret = Node(value.val,value.next)
else:
ret = Node.build(value)
if tmp.val:
ret.append(tmp)
self.val,self.next = ret.val,ret.next
return self
def cat(self, other, flag=True):
'''节点拼接，默认为追加，flag=Flase时插在头节点前'''
tmp = Node.build(other)
if flag:
ret = Node.build(self.values+tmp.values)
else:
ret = Node.build(tmp.values+self.values)
self.val,self.next = ret.val,ret.next
return self
def build(*data):
'''多参数创建节点链，参数允许为可迭代对象'''
values = []
for d in data:
if hasattr(d,'__iter__'):
for i in d:
values.append(i)
elif type(d) is Node:
values.extend(d.values)
else:
values.append(d)
cur = Node(values[-1])
for value in values[:-1][::-1]:
cur = Node(value, cur)
return cur
其中build()允许多参数输入；其它三个方法均允许可迭代对象作参数：
>>> node = Node.build(range(1,5),5,(6,7),[8])
>>> node
Node(1->2->3->4->5->6->7->8->None)
>>> a = Node.build(1,2,3)
>>> b = Node.build(4,5)
>>> a.cat(b)
Node(1->2->3->4->5->None)
>>> a.cat(b,flag=False)
Node(4->5->1->2->3->4->5->None)
>>> a = Node.build(1,2,3)
>>> a.append(4)
Node(1->2->3->4->None)
>>> a.append(range(5,8))
Node(1->2->3->4->5->6->7->None)
>>> a.append([8,9])
Node(1->2->3->4->5->6->7->8->9->None)
>>> a = Node.build(1,2,3)
>>> a.push(4)
Node(4->1->2->3->None)
>>> a.push(range(5,8))
Node(5->6->7->4->1->2->3->None)
>>> a.push([8,9])
Node(8->9->5->6->7->4->1->2->3->None)
>>> 有了拼接的方法，就可以尝试一下加法和乘法的重载——
拓展六：重载算术运算符
重载的约定：加法为两个节点的链的拼接；乘法为数乘，即一个节点链与一个正整数n相乘等价于反复n次相接，与0乘则为清空。乘法要注意分左乘和右乘，没有右乘方法整数在左边运算时会出错，代码如下放到拓展五中代码中即可：
def __add__(self, other):
if type(other) is not Node:
raise 'another Node typeError'
ret = Node.build(self.values+other.values)
return ret
def __mul__(self, other):
if type(other) is not int:
raise 'Integer typeError'
if other==0:
return Node()
elif other>0:
tmp = Node(self.val,self.next)
return Node.build(tmp.values * other)
else:
raise 'Integer rangeError'
def __rmul__(self,other):
return self.__mul__(other)
拓展七：添加其他方法
有增加必有减少，常见的操作除了创建、追加、插入，还有弹出、删除、查找、反序等等。有了以上的经验，给这个类添加这些方法不是难事，在以后的续篇中再来添加这些方法。
拓展八：增加单链表类
单链表是多个节点相接的线性列表，基本就是调用Node()方法来操作数据。省略的代码如下：
class Node():
def __init__(self, value=None, Next=None):
self.value = value
self.next = Next
def __repr__(self):
return f'Node({self.value})'
#......略......
class List():
def __init__(self, node=None):
if not hasattr(node,'__iter__'):
self.data = Node(node)
else:
self.data = None
for val in node:
self.append(val)
def __str__(self):
return f'List({self.__items__()})'
__repr__ = __str__
def __items__(self):
if self.is_empty():
return None
else:
res,cur = [],self.data
while cur is not None:
res.append(cur.value)
cur = cur.next
return res
def __getitem__(self, key):
lst = self.values
return lst[key]
def __len__(self):
if self.data is None:
return 0
return len(self.__items__())
def is_empty(self):
return self.data is None
size = __len__
def push(self, val):
node = Node(val)
node.next = self.data
self.data = node
def append(self, val):
if self.is_empty():
return self.push(val)
node = self.data
while node.next is not None:
node = node.next
node.next = Node(val)
def pop(self):
if self.is_empty():
return None
if self.size()==1:
self.next = None
node = self.data
while node.next is not None:
node = node.next
node.next = Node(val)
return
def clear(self):
self.data = None
def pprint(self):
if self.data==None:
print('None')
return
for i,v in enumerate(self.__items__()):
t = f"'{v}'" if type(v) is str else v
print(f'{t}->' if i<self.size()-1 else f'{t}->None',end='')
#......略......
大致的结构如上，未完善全部功能。如果把代码存入一个文本文件，如 linkedlist.py；以后只要导入这个就能用这些方法来编程了：
import linkedlist
node = linkedlist.Node.build(1,2,3,4)
print(node)#...... 或者：
from linkedlist import Node
node = Node()
node.add([1,2,3])
print(node)
本文完，以上所有代码只求实现效果，没有太多讲究算法优化。有空再来继续研究吧......
续篇已完工： 《触“类”旁通2｜数据结构入门之单链表的创建和遍历》
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