python实现的列表操作

class Node:
"""Single node in a data structure"""

def __init__(self, data):
"""Node constructor"""

self._data = data
self._nextNode = None

def __str__(self):
"""Node data representation"""

return str(self._data)

class List:
"""Linked list"""

def __init__(self):
"""List constructor"""

self._firstNode = None
self._lastNode = None

def __str__(self):
"""List string representation"""

if self.isEmpty():
return "empty"

currentNode = self._firstNode
output = []

while currentNode is not None:
output.append(str(currentNode._data))
currentNode = currentNode._nextNode

return " ".join(output)

def insertAtFront(self, value):
"""Insert node at front of list"""

newNode = Node(value)

if self.isEmpty():  # List is empty
self._firstNode = self._lastNode = newNode
else:   # List is not empty
newNode._nextNode = self._firstNode
self._firstNode = newNode

def insertAtBack(self, value):
"""Insert node at back of list"""

newNode = Node(value)

if self.isEmpty():  # List is empty
self._firstNode = self._lastNode = newNode
else:  # List is not empty
self._lastNode._nextNode = newNode
self._lastNode = newNode

def removeFromFront(self):
"""Delete node from front of list"""

if self.isEmpty():  # raise exception on empty list
raise IndexError, "remove from empty list"

tempNode = self._firstNode

if self._firstNode is self._lastNode:  # one node in list
self._firstNode = self._lastNode = None
else:
self._firstNode = self._firstNode._nextNode

return tempNode

def removeFromBack(self):
"""Delete node from back of list"""

if self.isEmpty():  # raise exception on empty list
raise IndexError, "remove from empty list"

tempNode = self._lastNode

if self._firstNode is self._lastNode:  # one node in list
self._firstNode = self._lastNode = None
else:
currentNode = self._firstNode

# locate second-to-last node
while currentNode._nextNode is not self._lastNode:
currentNode = currentNode._nextNode

currentNode._nextNode = None
self._lastNode = currentNode

return tempNode

def isEmpty(self):
"""Returns true if List is empty"""

return self._firstNode is None