匿名函数
fun = lambda x : x*2 print(fun) print(fun(2)) >>> <function <lambda> at 0x10b9197a0> >>> 4 说明： fun ->函数名 lambda ->相当于定义函数的def, 匿名函数的定义就用lambda x -> 匿名函数的形参 x * 2 ―> 匿名函数返回值
匿名函数的特点：临时存在，用完就没了
匿名函数的应用：一般与内置函数一起连用。
name_list = ['jason', 'tank', 'egon'] salary_list = [100, 200, 300] dic = {k:v for k, v in zip(name_list, salary_list)} #找出dic中工资最高的那个人的人名 print(max(dic, key=lambda name: dic[name])) >>>egon 内置函数
filter:
class filter(object): """ filter(function or None, iterable) --> filter object Return an iterator yielding those items of iterable for which function(item) is true. If function is None, return the items that are true. def fun(x): return x % 2 print(list(filter(fun, [1,2,3,4]))) >>> [1, 3]
def fun(x): if x % 2: return False return True print(list(filter(fun, [1,2,3,4]))) # (item for item in iterable if function(item)) >>>[2, 4]
map:
map(function,iterable,...)
Return an iterator that appliesfunctioniterable, yielding the results.
如果有多个iterable, 取多组iterable的第一个、第二个...组成一个个元组传给function。
With multiple iterables, the iterator stops when the shortest iterable is exhausted
只有一个iterable，map相当于把function作用到iterable的每一个元素上。
iterable_list = [1,2,3,12] print(list(map(lambda x:x*x, iterable_list))) >>> [1, 4, 9, 144]
不算是内置函数的reduce
functools.reduce(function,iterable[,initializer])- Applyfunctionsequence, from left to right,
- so as to reduce the sequence to a single value.
- For example,
calculates((((1+2)+3)+4)+5).
from functools import reduce l = [1, 2, 3, 4] def func(x, y): return x * y res = reduce(func, l) print(res) >>> 24
zip:
把每一个迭代器的元素聚合起来，返回一个元组
zip(*iterables)
1、Make an iterator that aggregates elements from each of the iterables.
Returns an iterator of tuples
x = [1, 2, 3, 4] y = [1, 2, 3, 4] res = zip(x, y) print(*res) >>> (1, 1) (2, 2) (3, 3) (4, 4)
x = [1, 2, 3, 4]y = [1, 2, 3, 4]res = zip(x, y)print(list(zip(*res)))>>> [(1, 2, 3, 4), (1, 2, 3, 4)]
2、The iterator stops when the shortest input iterable is exhausted.
3、With a single iterable argument, it returns an iterator of 1-tuples.
4、With no arguments, it returns an empty iterator