面试题0010

看代码写结果，内存中的列表

def  extendList(val,li =[]):
    li.append(val)
    return li

list1 = extendList(10)
list2 = extendList(123,[])
list3 = extendList('a')

print(list1)
print(list2)
print(list3)

[10, 'a']
[123]
[10, 'a']

参数变量在编译时会生成，而且只会生成一次，其内存地址的指向不发生变化，所以会有默认的[]

1和3都会使用默认的编译生成的同一个[]

2新生成一个[]

一行代码生成九九乘法表

print('\n'.join([' '.join(['{}*{} = {}'.format(x,y,x*y) for y in range(1,x+1)]) for x in range(1,10)]))

分解

[x for x in range(1,10)]

[([x*y for y in range(1,x+1)]) for x in range(1,10)]

[(['{}*{} = {}'.format(x,y,x*y) for y in range(1,x+1)]) for x in range(1,10)]

[' '.join(['{}*{} = {}'.format(x,y,x*y) for y in range(1,x+1)]) for x in range(1,10)]

'\n'.join([' '.join(['{}*{} = {}'.format(x,y,x*y) for y in range(1,x+1)]) for x in range(1,10)])

合并两个列表，不能有重复元素

alist = ['a','b','c','d','e','f']
blist = ['x','y','z','d','e','f']

def merge_list(*args):
    s = set()
    for i in args:
        s = s.union(i)
    return list(s)

merge_list(alist,blist)
>>>['z', 'f', 'x', 'y', 'd', 'c', 'a', 'e', 'b']

def merge_list(*args):
    q = []
    for i in args:
        q = q + i
    return list(set(q))

merge_list(alist,blist)
>>>['z', 'd', 'c', 'x', 'e', 'y', 'b', 'f', 'a']

一行代码实现对列表a中的偶数位置(索引号)的元素进行加3后求和

testlist = [1,2,3,4,5,6,7,8]
result =sum(map(lambda x:testlist[x]+3,filter(lambda x:x%2==0,range(len(testlist)))))
print(result)
>>>28

sum(list(map(lambda x:x+3,testlist[0::2])))

sum([testlist[x] + 3 for x in range(len(testlist)) if x % 2 == 0])

sum([x+3 for x in testlist[0::2]])