关于函数

关于函数:

1. 创建一个函数

def f():

    pass

2. 调用函数

def f():

    pass

f()

3. 函数的返回值

a. 没有设定返回值

def f():

    pass

print(f())   #None

b. 单个返回值

def f():

    return 1

print(f())

c. 多个返回值

def f():

return 1,2,"f"

print(f())

print(type(f()))

# (1, 2, 'f')

# <class 'tuple'>

 

4. 高阶函数

def f(num):

    return num**num

def fun(a,b,func):

    return func(a)+func(b)

res=fun(2,5,f)

print(res)

5. 关于递归

特性:

a. 调用自身函数

b. 有结束条件

c. 能用递归解决的问题,都可以循环解决.

d. 效率比循环低…不太建议使用

def fuc(n):

    """求n的阶乘"""

    if n==1:

        return 1

    return n*fuc(n-1)

print(fuc(20))

 

eg: 斐波那契数列 

def fun(n):

    if n==1 or n==2:

        return 1

    return fun(n-1)+fun(n-2)

 

for i in range(1,20):

    print(fun(i))

 

6. 内置函数

https://docs.python.org/3.5/library/functions.html

Built-in Functions
abs()	dict()	help()	min()	setattr()
all()	dir()	hex()	next()	slice()
any()	divmod()	id()	object()	sorted()
ascii()	enumerate()	input()	oct()	staticmethod()
bin()	eval()	int()	open()	str()
bool()	exec()	isinstance()	ord()	sum()
bytearray()	filter()	issubclass()	pow()	super()
bytes()	float()	iter()	print()	tuple()
callable()	format()	len()	property()	type()
chr()	frozenset()	list()	range()	vars()
classmethod()	getattr()	locals()	repr()	zip()
compile()	globals()	map()	reversed()	__import__()
complex()	hasattr()	max()	round()
delattr()	hash()	memoryview()	set()

 

 

 

1. filter

def f(v):

    if v !="a":

        return v

ret=filter(f,"abdasdsf")

print(tuple(ret))

 

1. map()

def ff(v):

    return  v+"map"

 

 

ret1 = map(ff,"abdasdsf")

print(list(ret1))

# ['amap', 'bmap', 'dmap', 'amap', 'smap', 'dmap', 'smap', 'fmap']

 

1. 对比map和filter

def f(v):     if v !="a":         return v ret=filter(f,"abdasdsf") print(tuple(ret)) # ('b', 'd', 's', 'd', 's', 'f')   def ff(v):     return  v+"map"     ret1 = map(ff,"abdasdsf") print(list(ret1)) # ['amap', 'bmap', 'dmap', 'amap', 'smap', 'dmap', 'smap', 'fmap']

def f(v):     if v !="a":         return v ret=map(f,"abdasdsf") print(tuple(ret)) # (None, 'b', 'd', None, 's', 'd', 's', 'f')   def ff(v):     return  v+"map"     ret1 = filter(ff,"abdasdsf") print(list(ret1)) # ['a', 'b', 'd', 'a', 's', 'd', 's', 'f']

 

1. reduce

(⊙o⊙)…,reduce貌似只支持两个值得操作

from functools import reduce

def f(a,b):

    return a*b

print(reduce(f,range(1,10)))

 

 

```````````````````````````````````````````分割线``````````````````````````````````````

在有三个参数的时候就会报错:

from functools import reduce

def f(a,b,c):

    return a+b+c

print(reduce(f,"hello"))

TypeError: f() missing 1 required positional argument: 'c'

 

Process finished with exit code 1

 

 

1. lambda

In [55]: f=lambda a :a+1

 

In [56]: f

Out[56]: <function __main__.<lambda>>

 

In [57]: f(2)

Out[57]: 3

 

Eg:与reduce一起使用实现阶乘

from functools import reduce

ret=reduce(lambda x,y: x*y,range(1,10))

print(ret)