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) 1 2 3 (5, 6, 7) {'foo': 1, 'bar': 2} >>> print_params_4(1,2) 1 2 3 () {}
调用元组、字典
>>> def add(x,y):return x+y >>> params=(1,2) >>> add(*params) 3 >>> 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']) 26
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) 1 3 4 Hi Hello >>> call_foo(*d,**f) Calling foo! 1 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) 8 >>> power(y=3,x=2) 8 >>> params=(5,)*2 >>> power(*params) 3125 >>> power(3,3,'Helld,world') Received redundant parameters: ('Helld,world',) 27 >>> 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) 81
修改全局变量
>>> def f(): global x x=x+1 >>> f() >>> x 2 >>> f() >>> x 3
嵌套
>>> def multiplier(factor): def multiplyByFactor(number): return number*factor return multiplyByFactor >>> double=multiplier(2) >>> double(5) 10 >>> multiplier(2*5) <function multiplyByFactor at 0x0000000002F8C6D8> >>> multiplier(2)(5) 10
递归（调用）
阶乘和幂
>>> def factorial(n): if n==1: return 1 else: return n*factorial(n-1) >>> factorial(5) 120 >>> 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) 8
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) 5
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) 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) 3 >>> def sum(x,y=6):return x+y >>> sum2=lambda x,y=6:x+y >>> sum2(4) 10
>>> 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