Python小练习 (2)

自定义sort函数

1. 源码实现sort函数

def sort(self, key=None, reverse=False): # real signature unknown; restored from __doc__
    """ L.sort(key=None, reverse=False) -> None -- stable sort *IN PLACE* """
    pass
key参数表示排序的规则,可传入一个函数
reverse表示是否反序,传入True或False

2. 基本功能的实现

def sort(iterable,*,key=None,reverse=False):
    newlist = []
    for x in iterable:
        for i,y in enumerate(newlist):
            if x>y:
                newlist.insert(i,x)
                break
        else:
            newlist.append(x)
    return newlist

lst = [43,1,5,23,12,10]
print(1,lst)
print('*'*30)
print(2,sort(lst))

# 程序运行结果
1 [43, 1, 5, 23, 12, 10]
******************************
2 [43, 23, 12, 10, 5, 1]

3. reverse参数的实现

def sort(iterable,*,key=None,reverse=False):
    newlist = []
    for x in iterable:
        for i,y in enumerate(newlist):
            comp = x > y if reverse else x < y
            if comp:
                newlist.insert(i,x)
                break
        else:
            newlist.append(x)
    return newlist

lst = [43,1,5,23,12,10]
print(1,lst)
print('*'*30)
print(2,sort(lst))

# 程序运行结果
1 [43, 1, 5, 23, 12, 10]
******************************
2 [1, 5, 10, 12, 23, 43]

4. key参数的实现

def sort(iterable,*,key=lambda x:6-x,reverse=False):
    newlist = []
    for x in iterable:
        cx = key(x) if key else x
        for i,y in enumerate(newlist):
            cy = key(y) if key else y
            comp = cx > cy if reverse else cx < cy
            if comp:
                newlist.insert(i,x)
                break
        else:
            newlist.append(x)
    return newlist

lst = [43,1,5,23,12,10]
print(1,lst)
print('*'*30)
print(2,sort(lst))

# 程序运行结果
1 [43, 1, 5, 23, 12, 10]
******************************
2 [43, 23, 12, 10, 5, 1]

filter函数介绍

lst1 = [100,42,3,5,45,23,65]
lst = list(filter(lambda x: x%3==0,lst1))
print(1,lst)
print(2,list(filter(None,range(5))))
print(3,list(filter(None,range(-5,5))))

# 程序运行结果
1 [42, 3, 45]
2 [1, 2, 3, 4]
3 [-5, -4, -3, -2, -1, 1, 2, 3, 4]

映射map函数介绍

lst1 = [100,42,3,5,45,23,65]
print(1,list(map(lambda x:2*x+1,lst1)))
print(2,dict(map(lambda x:(x%5,x),range(500))))
print(3,dict(map(lambda x,y:(x,y),'abcde',range(10))))

# 程序运行结果
1 [201, 85, 7, 11, 91, 47, 131]
2 {0: 495, 1: 496, 2: 497, 3: 498, 4: 499}
3 {'a': 0, 'b': 1, 'c': 2, 'd': 3, 'e': 4}