002_第三部分_[函数 / 高阶函数 / 装饰器]
[TOC]
一.高阶函数:
顺序排序
enumerate([1,2 ,3 , 4, 5])
for idx, item in enumerate([1, 2, 3, 4]):
print(idex)
print(item)
def sort(*args):
ret = []
for item in args:
for i, v in enumerate(ret):
if item > v:
ret.insert(i,item)
break
else:
ret.append(item)
return ret
sort(3, 1, 2, 5)逆序排列
def sort(f, *args):
ret = []
for item in args:
for i, v in enumerate(ret):
if f:
if item >= v:
ret.insert(i,item)
break
else:
if item <= v:
ret.insert(i,item)
break
else:
ret.append(item)
return ret
sort(True, 3, 1, 2, 5)高阶函数
def sort(cmp, *args):
ret = []
for item in args:
for i, v in enumerate(ret):
if cmp(item, v):
ret.insert(i, item)
break
else:
ret.append(item)
return ret
def cmp1(x, y):
return x >= y
def cmp2(x, y):
return x <= y
sort(cmp1, 3, 1, 2, 5)
[5, 3, 2, 1]二.特殊函数[内置函数]:
1.filter 根据布尔返回值,输出返回值为True的数值:
def bigger_5(x):
if x > 5:
return True
return False
filter(bigger_5, range(10))
list(filter(bigger_5, range(10)))
>[6, 7, 8, 9]2.map 输出函数中的返回值的一个迭代器:
格式：map( func, seq1[, seq2...] )
例子1:
def bigger_5(x):
if x > 5:
return True
return False
map(bigger_5, range(10))
list(map(bigger_5, range(10)))
>[False, False, False, False, False, False, True, True, True, True]例子2:
def inc(x):
return x + 1
list(map(inc,[1, 2, 3, 4]))
>[2, 3, 4, 5]
list(map(inc,range(3)))
>[1, 2, 3]例子3:
list(map(lambda x:x + 1,range(3)))
>[1, 2, 3]例子4:
a = map(lambda x:x + 1,range(3))
next(a)
>1
next(a)
>2
next(a)
>3
next(a)
>StopIteration3.reduce
格式：reduce( func, seq[, init] )
reduce函数即为化简，它是这样一个过程：每次迭代，将上一次的迭代结果（第一次时为init的元素，如没有init则为seq的第一个元素）与下一个元素一同执行一个二元的func函数。在reduce函数中，init是可选的，如果使用，则作为第一次迭代的第一个元素使用。
n = 5
print reduce(lambda x, y: x * y, range(1, n + 1)) # 120m = 2
n = 5
print reduce( lambda x, y: x * y, range( 1, n + 1 ), m ) # 2404.lambda:
def sort(cmp, *args):
ret = []
for item in args:
for i, v in enumerate(ret):
if cmp(item, v):
ret.insert(i, item)
break
else:
ret.append(item)
return ret
sort(lambda x, y: x >= y, 3, 1, 2, 5)5.函数作为返回值
def make_ic(f=1):
def inc(x):
return x + f
return inc
inc1 = make_ic(1)
inc1(5)
>6柯里化:
def bigger(x):
def inner_bigger(y):
return y > x
return inner_bigger
list(filter(bigger(5), range(10)))
>[6, 7, 8, 9]三.functools库
1.partial [设置默认参数, 后期任然可以通过关键字参数进行传参]
查看是不是可调用对象:
from functools import partial
import pymysql
callable(bigger_3)
bigger_3 = partial(bigger,y=3)
connect = partial(pymysql.connect, user='root', password='xxxx', database='xxxx', port=3306)
connect(host='127.0.0.1')四.装饰器
装饰器的本质就是一个函数,这个函数接收一个函数作为参数, 返回一个函数,通常,返回的这个函数,是对传入的函数执行前后增加了一些语句,所以叫做装饰;
1.普通装饰器
#第一种写法
def timeit(fn):
def wrap(*args, **kwargs):
start = time.time()
ret = fn(*args,**kwargs)
print(time.time() - start)
return ret
return wrap
def sleep(x):
time.sleep(x)
timeit(sleep)(3)
第二种方法:
def timeit(fn):
def wrap(*args, **kwargs):
start = time.time()
ret = fn(*args,**kwargs)
print(time.time() - start)
return ret
return wrap
@timeit
def sleep(x):
time.sleep(x)
sleep(3)time.time() //得到的是一个自然的时间
time.clock() //得到的是一个cpu执行时间,占用cpu的时间;
2.带参数的装饰器
import time
def timeit(process_time=False):
cacl = time.clock if process_time else time.time
def inner_timeit(fn):
def wrap(*args, **kwargs):
start = cacl
ret = fn(*args, **kwargs)
print(cacl() - start)
return ret
return wrap
return inner_timeit
@timeit(True)
def sleep(x):
time.sleep(x)
sleep(3)import time
def timeit(process_time=False):
cacl = time.clock if process_time else time.time
def inner_timeit(fn):
def wrap(*args, **kwargs):
start = cacl()
ret = fn(*args, **kwargs)
print(cacl() - start)
return ret
return wrap
return inner_timeit
def sleep(x):
time.sleep(x)
timeit(False)(sleep)(3) 等价 timeit()(sleep)(3)
timeit(True)(sleep)(3)import time
def timeit(process_time=False):
cacl = time.clock if process_time else time.time
def inner_timeit(fn):
def wrap(*args, **kwargs):
start = cacl()
ret = fn(*args, **kwargs)
print(cacl() - start)
return ret
return wrap
return inner_timeit
@timeit(True) or @timeit() or @timeit(False)
def sleep(x):
time.sleep(x)
sleep(3)#带参数的装饰器的基本结构
def make_timeit():
def timeit():
def inner_timeit(fn):
def wrap(*args, **kwargs):
return fn(*args, **kwargs)
return wrap
return inner_timeit
return timeit
@make_timeit()() //这样写是有问题的,因为python的语法解析器只支持带一个参数
正确写法如下
time_2 = make_timeit()
@time_2()
或者
time_2 = make_timeit()()
@time_2
def fn():
pass3.装饰器的实际应用:
flask使用了大量的装饰来做路由
[flask.pocoo.org]
#利用装饰器进行权限控制
def check(allows):
def deco(fn):
def wrap(username, *args, **kwargs):
if username in allows:
return fn(username, *args, **kwargs) //这一行需要和wrap这一行一一对应起来
return "not allow"
return wrap
return deco
@check(["comyn", "mage"])
def private(username):
print("congratulation")
private("comyn")4.函数的字文档[wraps]:
def test():
'''
this is test
@return None
'''
pass
help(test)
>Help on function test in module __main__:
test()
this is test
@return Noneimport time
def timeit(process_time=False):
cacl = time.clock if process_time else time.time
def inner_timeit(fn):
def wrap(*args, **kwargs):
start = cacl()
ret = fn(*args, **kwargs)
print(cacl() - start)
return ret
wrap.__name__ = fn.__name__
wrap.__doc__ = fn.__doc__
return wrap
return inner_timeit
@timeit(True) or @timeit() or @timeit(False)
def sleep(x):
'''
this is test
'''
sleep.__name__
help(sleep)# 使用wraps实现函数的字文档
import time
from functools import wraps
def timeit(process_time=False):
cacl = time.clock if process_time else time.time
@wraps()
def inner_timeit(fn):
def wrap(*args, **kwargs):
start = cacl()
ret = fn(*args, **kwargs)
print(cacl() - start)
return ret
return wrap
return inner_timeit
@timeit(True) or @timeit() or @timeit(False)
def sleep(x):
'''
this is test
'''
sleep.__name__
help(sleep)