python学习记录（二）-特殊函数

闭包函数

def outer():
    var = 100
    def inner():
        nonlocal var
        var += 200
        print(var)
    return inner

res = outer()
res() # 300

lambda表达式

res = lambda x,y:x+y
print(res(1,2)) #3
res = lambda sex:'男' if sex == 'male' else '女'
print(res('female')) # 女

迭代器

可迭代对象：str,list,dict,tuple,set,range()

迭代器取值特点：取出一个少一个，直到取完，再取就报错

迭代器取值方式：

1、next()：一次取一个数据

2、list()：取出所有数据

3、for循环

var = [1,2]
res = iter(var)
#print(res,type(res)) # <list_iterator object> <class 'list_iterator'>
print(next(res)) # 1
print(next(res)) # 2
#print(next(res)) # StopIteration
print(list(res)) # []

检测可迭代对象和迭代器

from collections.abc import Iterable,Iterator
var = '1234'
res = iter(var)
r1 = isinstance(var,Iterable) # 检测是否是可迭代对象
r2 = isinstance(var,Iterator) # 检测是否是迭代器
r3 = isinstance(res,Iterable)
r4 = isinstance(res,Iterator)
print(r1,r2) # True False
print(r3,r4) # True True

zip函数

var1 ='1234'
var2 =['a','b','c','d']
print(zip(var1,var2)) # <zip object at 0x0000027E3422F0C8>
print(*zip(var1,var2)) # ('1', 'a') ('2', 'b') ('3', 'c') ('4', 'd')
print(list(zip(var1,var2))) # [('1', 'a'), ('2', 'b'), ('3', 'c'), ('4', 'd')]
x,y = zip(*zip(var1,var2))
print(x,y) # ('1', '2', '3', '4') ('a', 'b', 'c', 'd')

ascii码

print(ord('a')) # 97
print(chr(97)) # a

sorted()函数

def fun(num):
    return abs(num)
varlist = [4,2,8,-3]
print(sorted(varlist)) # [-3, 2, 4, 8]
print(sorted(varlist,reverse=True)) # [8, 4, 2, -3]
print(sorted(varlist,key=abs)) # [2, -3, 4, 8]
print(sorted(varlist,key=fun)) # [2, -3, 4, 8]
print(sorted(varlist,key=lambda x:abs(x))) # [2, -3, 4, 8]

map()函数

varlist = [1,2,3,4]
res = map(lambda x:x**2,varlist)
print(list(res)) # [1, 4, 9, 16]

reduce()函数

from functools import reduce
varlist = [5,2,1,1]
res = reduce(lambda x,y:x*10+y,varlist)
print(res) #5211

filter()函数

varlist = [1,2,3,4,5,6,7,8]
res = filter(lambda x:True if x % 2 == 0 else False,varlist)
print(list(res)) # [2, 4, 6, 8]