python中函数的详细说明

>>> fibs
[0, 1]>>> n=input(&＃39;How many Fibonacci numbers do your what?&＃39;)
How many Fibonacci numbers do your what?10
>>> for n in range(n-2):
    fibs.append(fibs[-2]+fibs[-1])    
>>> fibs
[0, 1, 1, 2, 3, 5, 8, 13, 21, 34]

注意：内建的callable函数可以用来判断函数是否可以调用

def 定义函数

>>> def hello(name):
    print "Hello"+name

    
>>> hello(&＃39;world&＃39;)
Helloworld

用函数写斐波拉希数列

>>> def fibs(num):
    s=[0,1]
    for i in range(num-2):
        s.append(s[-2]+s[-1])

        
>>> fibs(10)

注意：return语句从函数中返回值

函数说明：如果给函数写文档，让其他人能理解的话，可以加入注释（#开头）。另外一种方法就是直接写上字符串。

>>> def square(x):
    &＃39;Calculates the square of the number x.&＃39;
    return x*x

>>> square.__doc__
&＃39;Calculates the square of the number x.&＃39;

内建的help函数，可以得到关于函数，包括它的文档字符串信息

>>> help(square)
Help on function square in module __main__:

square(x)
    Calculates the square of the number x.

在函数内为参数赋予新值不会改变外部变量的值：

>>> def try_to_change(n):
    n=&＃39;Mr,Gumby&＃39;

    
>>> name=&＃39;Mrs,Entity&＃39;
>>> try_to_change(name)
>>> name
&＃39;Mrs,Entity&＃39;

字符串（以及数字和元组）是不可改变的，即无法修改。若将可改变的数据结构（列表或字典）修改，参数会被修改

>>> n=[&＃39;Bob&＃39;,&＃39;Alen&＃39;]
>>> def change(m):
    m[0]=&＃39;Sandy&＃39;

    
>>> change(n[:])
>>> n
[&＃39;Bob&＃39;, &＃39;Alen&＃39;]
>>> change(n)
>>> n
[&＃39;Sandy&＃39;, &＃39;Alen&＃39;]

关键字参数和默认值

>>> def hello(name,greeting=&＃39;Hello&＃39;,punctuation=&＃39;!&＃39;):
    print &＃39;%s,%s%s&＃39; % (greeting,name,punctuation)

    
>>> hello(name=&＃39;Nsds&＃39;)
Hello,Nsds!
>>> hello(name=&＃39;Nsds&＃39;,greeting=&＃39;Hi&＃39;)
Hi,Nsds!

收集参数

返回元组：

>>> def print_params(*params):
    print params

    
>>> print_params(&＃39;Testing&＃39;) #返回元组
(&＃39;Testing&＃39;,)
>>> print_params(1,2,3)
(1, 2, 3)
>>> def print_params_2(title,*params):
    print title
    print params

    
>>> print_params_2(&＃39;Params:&＃39;,1,2,3)
Params:
(1, 2, 3)

返回字典

>>> def print_params_3(**params):
    print params

    
>>> print_params_3(x=1,y=2,z=3)
{&＃39;y&＃39;: 2, &＃39;x&＃39;: 1, &＃39;z&＃39;: 3}
>>> def print_params_4(x,y,z=3,*pospar,**keypar):
    print x,y,z
    print pospar
    print keypar

    
>>> print_params_4(1,2,3,5,6,7,foo=1,bar=2)
2 3
(5, 6, 7)
{&＃39;foo&＃39;: 1, &＃39;bar&＃39;: 2}
>>> print_params_4(1,2)
2 3
()
{}

调用元组、字典

>>> def add(x,y):return x+y

>>> params=(1,2)
>>> add(*params)
>>> def with_stars(**kwds):
    print kwds[&＃39;name&＃39;],&＃39;is&＃39;,kwds[&＃39;age&＃39;],&＃39;years old&＃39;]
>>> def without_starts(kwds):
    print kwds[&＃39;name&＃39;],&＃39;is&＃39;,kwds[&＃39;age&＃39;],&＃39;years old&＃39;
>>> args={&＃39;name&＃39;:&＃39;Nsds&＃39;,&＃39;age&＃39;:24}
>>> with_stars(**args)
Nsds is 24 years old
>>> without_starts(args)
Nsds is 24 years old
>>> add(2,args[&＃39;age&＃39;])

星号只在定义函数（允许使用不定数目的参数）或者调用（"分割"字典或者序列）时才有用

>>> def foo(x,y,z,m=0,n=0):
    print x,y,z,m,n

    
>>> def call_foo(*args,**kwds):
    print "Calling foo!"
    foo(*args,**kwds)

>>> d=(1,3,4)
>>> f={&＃39;m&＃39;:&＃39;Hi&＃39;,&＃39;n&＃39;:&＃39;Hello&＃39;}
>>> foo(*d,**f)
3 4 Hi Hello
>>> call_foo(*d,**f)
Calling foo!
3 4 Hi Hello

几个例子

>>> def story(**kwds):
    return &＃39;Once upon a time,there was a&＃39; \
           &＃39;%(job)s called %(name)s.&＃39; % kwds

>>> def power(x,y,*others):
    if others:
        print &＃39;Received redundant parameters:&＃39;,others
    return pow(x,y)

>>> def interval(start,stop=None,step=1):
    if stop is None:
        start,stop=0,start  #start=0,stop=start
    result=[]
    i=start
    while i>> print story(job=&＃39;king&＃39;,name=&＃39;Gumby&＃39;)
Once upon a time,there was aking called Gumby.
>>> print story(name=&＃39;Sir Robin&＃39;,job=&＃39;brave knight&＃39;)
Once upon a time,there was abrave knight called Sir Robin.
>>> params={&＃39;job&＃39;:&＃39;language&＃39;,&＃39;name&＃39;:&＃39;Python&＃39;}
>>> print story(**params)
Once upon a time,there was alanguage called Python.
>>> del params[&＃39;job&＃39;]
>>> print story(job=&＃39;store of genius&＃39;,**params)
Once upon a time,there was astore of genius called Python.
>>> power(2,3)
>>> power(y=3,x=2)
>>> params=(5,)*2
>>> power(*params)
>>> power(3,3,&＃39;Helld,world&＃39;)
Received redundant parameters: (&＃39;Helld,world&＃39;,)
>>> interval(10)
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
>>> interval(1,5)
[1, 2, 3, 4]
>>> power(*interval(3,7))
Received redundant parameters: (5, 6)

修改全局变量

>>> def f():
    global x
    x=x+1

    
>>> f()
>>> x
>>> f()
>>> x

嵌套

>>> def multiplier(factor):
    def multiplyByFactor(number):
        return number*factor
    return multiplyByFactor

>>> double=multiplier(2)
>>> double(5)
>>> multiplier(2*5)

>>> multiplier(2)(5)

递归（调用）

阶乘和幂

>>> def factorial(n):
    if n==1:
        return 1
    else:
        return n*factorial(n-1)
    
>>> factorial(5)
>>> range(3)
[0, 1, 2]
>>> def power(x,n):
    result=1
    for i in range(n):
        result *= x
    return result
>>> power(5,3)

>>> def power(x,n):
    if n==0:
        return 1
    else:
        return x*power(x,n-1)

    
>>> power(2,3)

二元查找

>>> def search(s,n,min=0,max=0):
    if max==0:
        max=len(s)-1
    if min==max:
        assert n==s[max]
        return max
    else:
        middle=(min+max)/2
        if n>s[middle]:
            return search(s,n,middle+1,max)
        else:
            return search(s,n,min,middle)

        
>>> search(seq,100)

map函数

它接收一个函数和一个列表，并通过函数依次作用在list的每个元素上，得到一个新的list并返回

>>> map(str,range(10))
[&＃39;0&＃39;, &＃39;1&＃39;, &＃39;2&＃39;, &＃39;3&＃39;, &＃39;4&＃39;, &＃39;5&＃39;, &＃39;6&＃39;, &＃39;7&＃39;, &＃39;8&＃39;, &＃39;9&＃39;]
>>> def f(x):
    return x*x

>>> print map(f,[1,2,3,4,5,6,7])
[1, 4, 9, 16, 25, 36, 49]

>>> def format_name(s):
    s1=s[0].upper()+s[1:].lower()
    return s1

>>> print map(format_name,[&＃39;ASDF&＃39;,&＃39;jskk&＃39;])
[&＃39;Asdf&＃39;, &＃39;Jskk&＃39;]

filter函数

它接收一个函数和一个列表(list)，这个函数依次对每个元素进行判断，返回 True或 False，filter()根据判断结果自动过滤掉不符合条件的元素，返回由符合条件元素组成的新列表

>>> def is_not_empty(s):
    return s and len(s.strip())>0

>>> filter(is_not_empty,[None,&＃39;dshk&＃39;,&＃39;  &＃39;,&＃39;sd&＃39;])
[&＃39;dshk&＃39;, &＃39;sd&＃39;]
>>> def pfg(x):
    s=math.sqrt(x)
    if s%1==0:
        return x

>>> import math
>>> pfg(100)
>>> pfg(5)
>>> filter(pfg,range(100))
[1, 4, 9, 16, 25, 36, 49, 64, 81]
>>> def is_sqr(x):
    return math.sqrt(x)%1==0

>>> is_sqr(100)
True
>>> filter(is_sqr,range(100))
[0, 1, 4, 9, 16, 25, 36, 49, 64, 81]

lambda函数

也叫匿名函数，即，函数没有具体的名称,而用def创建的方法是有名称的

>>> def foo():return &＃39;Begin&＃39;

>>> lambda:&＃39;begin&＃39;
 at 0x0000000002ECC2E8>
>>> s=lambda:&＃39;begin&＃39;
>>> print s()
begin
>>> s= lambda x,y:x+y
>>> print s(1,2)
>>> def sum(x,y=6):return x+y

>>> sum2=lambda x,y=6:x+y
>>> sum2(4)

>>> filter(lambda x:x*x,range(1,5))
[1, 2, 3, 4]>>> map(lambda x:x*x,range(1,5))
[1, 4, 9, 16]>>> filter(lambda x:x.isalnum(),[&＃39;8ui&＃39;,&＃39;&j&＃39;,&＃39;lhg&＃39;,&＃39;)j&＃39;])
[&＃39;8ui&＃39;, &＃39;lhg&＃39;]

reduce函数

它接收一个函数和一个列表(list)，函数必须接收两个参数，这个函数依次对列表每个元素进行调用，返回结果值组成的新列表

>>> reduce(lambda x,y:x*y,range(1,5))
24
>>> reduce(lambda x,y:x+y,[23,9,5,6],100) #初始值为100，依次相加列表中的值
143

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