python中函数的详细说明

斐波拉希数列

>>> fibs[0, 1]>>> n=input('How many Fibonacci numbers do your what?')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('world')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

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是直接写上字符串。

>>> def square(x):    'Calculates the square of the number x.'    return x*x>>> square.__doc__'Calculates the square of the number x.'

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='Mr,Gumby'    >>> name='Mrs,Entity'>>> try_to_change(name)>>> name'Mrs,Entity'

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=['Bob','Alen']>>> def change(m):    m[0]='Sandy'    >>> change(n[:])>>> n['Bob', 'Alen']>>> change(n)>>> n['Sandy', 'Alen']

关键字参数和默认值

>>> def hello(name,greeting='Hello',punctuation='!'):    print '%s,%s%s' % (greeting,name,punctuation)    >>> hello(name='Nsds')Hello,Nsds!>>> hello(name='Nsds',greeting='Hi')Hi,Nsds!

收集参数

返回元组：

>>> def print_params(*params):    print params    >>> print_params('Testing') #返回元组('Testing',)>>> print_params(1,2,3)(1, 2, 3)>>> def print_params_2(title,*params):    print title    print params    >>> print_params_2('Params:',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){'y': 2, 'x': 1, 'z': 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){'foo': 1, 'bar': 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['name'],'is',kwds['age'],'years old']>>> def without_starts(kwds):    print kwds['name'],'is',kwds['age'],'years old'>>> args={'name':'Nsds','age':24}>>> with_stars(**args)Nsds is 24 years old>>> without_starts(args)Nsds is 24 years old>>> add(2,args['age'])

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={'m':'Hi','n':'Hello'}>>> 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 'Once upon a time,there was a' \           '%(job)s called %(name)s.' % kwds>>> def power(x,y,*others):    if others:        print 'Received redundant parameters:',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<stop:        result.append(i)        i+=step    return result>>> print story(job='king',name='Gumby')Once upon a time,there was aking called Gumby.>>> print story(name='Sir Robin',job='brave knight')Once upon a time,there was abrave knight called Sir Robin.>>> params={'job':'language','name':'Python'}>>> print story(**params)Once upon a time,there was alanguage called Python.>>> del params['job']>>> print story(job='store of genius',**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,'Helld,world')Received redundant parameters: ('Helld,world',)>>> 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)<function multiplyByFactor at 0x0000000002F8C6D8>>>> 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))['0', '1', '2', '3', '4', '5', '6', '7', '8', '9']>>> 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,['ASDF','jskk'])['Asdf', 'Jskk']

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,'dshk','  ','sd'])['dshk', 'sd']>>> 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 'Begin'>>> lambda:'begin'<function <lambda> at 0x0000000002ECC2E8>>>> s=lambda:'begin'>>> 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(),['8ui','&j','lhg',')j'])['8ui', 'lhg']

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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