Python3怎么实现自定义比较排序

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自定义比较排序/运算符

Python3和Python2相比有挺多变化。

在Python2中可以直接写一个cmp函数作为参数传入sort来自定义排序，但是Python3取消了。

在这里总结一下Python3的自定义排序的两种写法，欢迎补充。

我们以二维空间中的点来作为待排序的数据结构，我们希望能先比较x后再比较y。

class Pos:    def __init__(self, x = 0, y = 0):        self.x = x        self.y = y     def __str__(self):        return ('(%s, %s)' % (self.x, self.y))     __repr__ = __str__

1.cmp函数

第一种方法我们还是以重写cmp或lambda表达式的形式，和Python2很类似

注意，此方法用sorted是不能成功排序的

只是要借助functools

import functoolsdef cmp(a, b):    return a.x-b.x if a.x != b.x else a.y-b.y  # x y均按照从小到大的顺序 if __name__ == '__main__':     test_list = [Pos(5, 1), Pos(2,5), Pos(2, 4)]    # test_list.sort(key=functools.cmp_to_key(lambda a,b: a.x-b.x if a.x != b.x else a.y-b.y))    test_list.sort(key=functools.cmp_to_key(cmp))    # sorted(test_list, key=functools.cmp_to_key(cmp))  #    亲测此方法不能成功排序    print(test_list)  # 输出结果 [(2, 4), (2, 5), (5, 1)]

2.重写类方法

Python2中可以直接重写__cmp__方法来实现比较，但是Python3中已经取消了.

Python3中需要细分每一个比较运算符.

__lt__: <__gt__: >__ge__: >=__eq__: ==__le__: <=

实现如下

class Pos:    def __init__(self, x = 0, y = 0):        self.x = x        self.y = y     def __str__(self):        return ('(%s, %s)' % (self.x, self.y))     def __lt__(self, other):        print('lt: ' + str(self))        return self.x < other.x if self.x != other.x else self.y < other.y     def __gt__(self, other):        print('gt: ' + str(self))        return self.x > other.x if self.x != other.x else self.y > other.y     def __ge__(self, other):        print('ge: ' + str(self))        return self.x >= other.x if self.x != other.x else self.y >= other.y     def __eq__(self, other):        print('eq: ' + str(self))        return self.x == other.x and self.y == other.y     def __le__(self, other):        print('le: ' + str(self))        return self.x <= other.x if self.x != other.x else self.y <= other.y     __repr__ = __str__

我们实践一下

if __name__ == '__main__':     if Pos(5,1) <= Pos(2,4):        print('True!')    if Pos(5,1) == Pos(2,4):        print('True!')    if Pos(5,1) > Pos(2,4):        print('True!')# 输出# le: (5, 1)# eq: (5, 1)# gt: (5, 1)# True!

最后我们回到排序

if __name__ == '__main__':     test_list = [Pos(5, 1), Pos(2,5), Pos(2, 4)]    test_list.sort()    print(test_list)     test_list.sort(reverse=True)    print(test_list) # 输出# lt: (2, 5)# lt: (2, 4)# [(2, 4), (2, 5), (5, 1)]# lt: (2, 5)# lt: (2, 4)# [(5, 1), (2, 5), (2, 4)]

Python3实现各种排序方法

# coding=gbkimport randomfrom array import arraydef swap(lyst,i,j):    temp = lyst[i]    lyst[i] = lyst[j]    lyst[j] = temp#选择排序，复杂度O(n^2)def selectionSort(lyst):     i = 0    while i < len(lyst) - 1:        minIndex = i        j = i + 1        while j < len(lyst):            if lyst[j] < lyst[minIndex]:                minIndex = j            j += 1        if minIndex != i:            swap(lyst,minIndex,i)        i += 1#冒泡排序，复杂的O(n^2)def bubbleSort(lyst):    n = len(lyst)    while n > 1:        i = 1        while i < n:            if lyst[i] < lyst[i-1]:                swap(lyst,i,i-1)            i += 1        n -= 1#冒泡排序优化改进最好情况def bubbleSortWithTweak(lyst):    n = len(lyst)    while n > 1:        swapped = False        i = 1        while i < n:            if lyst[i] < lyst[i-1]:                swap(lyst,i,i-1)                swapped = True            i += 1        if not swapped: return        n -= 1#插入排序，复杂的O(n^2)def insertionSort(lyst):    i = 1    while i < len(lyst):        itemToInsert = lyst[i]        j = i - 1        while j >= 0:            if itemToInsert < lyst[j]:                lyst[j+1] = lyst[j]                j -= 1            else:                break        lyst[j+1] = itemToInsert        i += 1#快速排序,最好情况，复杂的O(n*(log2 n))，最坏情况，复杂的O(n^2)def quicksort(lyst):    quicksortHelper(lyst,0,len(lyst)-1)def quicksortHelper(lyst,left,right):    if left < right:        pivotLocation = partition(lyst,left,right)        quicksortHelper(lyst,left,pivotLocation-1)        quicksortHelper(lyst,pivotLocation+1,right)def partition(lyst,left,right):    middle = (left+right) // 2    pivot = lyst[middle]    lyst[middle] = lyst[right]    lyst[right] = pivot    boundary = left    for index in range(left,right):        if lyst[index] < pivot:            swap(lyst,index,boundary)            boundary += 1    swap(lyst,right,boundary)    return boundary#合并排序def mergeSort(lyst):    copyBuffer = [0]*(len(lyst))    mergeSortHelper(lyst,copyBuffer,0,len(lyst)-1)def mergeSortHelper(lyst,copyBuffer,low,high):    if low < high:        middle = (low+high)//2        mergeSortHelper(lyst,copyBuffer,low,middle)        mergeSortHelper(lyst,copyBuffer,middle+1,high)        merge(lyst,copyBuffer,low,middle,high)def merge(lyst,copyBuffer,low,middle,high):    i1 = low    i2 = middle + 1    for i in range(low,high+1):        if i1 > middle:            copyBuffer[i] = lyst[i2]            i2 += 1        elif i2 > high:            copyBuffer[i] = lyst[i1]            i1 += 1              elif lyst[i1] < lyst[i2]:            copyBuffer[i] = lyst[i1]            i1 += 1              else :            copyBuffer[i] = lyst[i2]            i2 += 1     for i in range(low,high+1):        lyst[i] = copyBuffer[i]def main(size = 20,sort = mergeSort):       lyst = []    for count in range(size):        lyst.append(random.randint(1,size+1))    print(lyst)    sort(lyst)    print(lyst)if __name__ == "__main__":    main()

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