第六章-抽象——python基础教程（第二版）笔记

进入稍难的部分了

6.3创建函数

终于自己写函数了

#斐波那契数列def fibs(num): #定义函数名和参数类型    result=[0,1] #初始化斐波那契的两项    for i in range(num-2):        result.append(result[-2]+result[-1])     return result  #返回结果是斐波那契最后一项print fibs(10)   #结果[0, 1, 1, 2, 3, 5, 8, 13, 21, 34]#6.3.1文档化函数def square(x):    "caculates the square of x"#函数说明    return x*xprint square(10)#结果100print help(square)#查看函数说明'''Help on function square in module __main__:square(x)    caculates the square of xNone'''#6.3.2并非真正函数的函数def test():    print "a"    return     print "b"x=test() print test()print x'''没看懂结果aaNoneNone'''

6.4参数魔法

#6.4.2变参#字符串（数字和元组)是不可变的def change(n):    n[0]="c"name=["a","b"]change(name)print name  #结果['c', 'b']#这个参数有点复杂，举个例子def story(**kwds):  #将**后面的参数转化为字典    return "once upon a time,there was a \%(b)s called %(a)s."%kwds    #连成一行def power(x,y,*others): #将*后的所有参数转化为列表    if others:        print "receieved redundant parameters:",others    return pow(x,y)def interval(start,stop=None,step=1):    "Imitates range() for step>0"    if stop is None:    #如果没有为stop提供值        start,stop=0,start #指定参数    result=[]    i=start     #计算start索引    while i<stop:   #直到计算到stop的索引        result.append(i)    #将索引添加到result内        i+=step         #用step(>0)增加索引i    return result#开始测试函数print story(a="A",b="B") #结果 once upon a time,there was a B called A.x={"a":"c","b":"d"}print story(**x)   #结果 once upon a time,there was a d called c.del x["a"]    #修改参数print story(a="e",**x)   #结果once upon a time,there was a d called e.print power(2,3)   #结果 8print power(x=2,y=3)  #结果 8x=(5,)*2  #序列乘2print power(*x)   #结果 3125print power(2,3,"hello world")'''结果receieved redundant parameters: ('hello world',)8'''print interval(5)   #结果 [0, 1, 2, 3, 4]print interval(1,5)   #结果[1, 2, 3, 4]print interval(3,12,4)   #结果[3, 7, 11]print power(*interval(3,7))'''结果receieved redundant parameters: (5, 6)81'''

6.5作用域

6.6递归

#6.6.1阶乘和幂#阶乘    #1.循环方法def factorial(n):    result=n    for i in range(1,n):        result*=i    return resultprint factorial(4)  #结果 24    #2.迭代方法def factorial(n):    if n==1:        return 1    else:     return n*factorial(n-1)print factorial(4)  #结果 24#幂    #1.循环方法def power(x,y):    result=1    for i in range(y):        result*=x    return resultprint power(2,3)  #结果 8    #2.迭代方法def power(x,y):    if y==0:        return 1    else:        return x*power(x,y-1)print power(2,3)  #结果 8#6.2.2二分查找法def search(sequence,number,lower=0,upper=None):    if upper is None:        upper=len(sequence)-1    if lower==upper:        assert number==sequence[upper]        return upper    else:        middle=(lower+upper)//2        if number>sequence[middle]:                return search(sequence,number,middle+1,upper)        else:                return search(sequence,number,lower,middle)seq=[12,141,123,14,12,2,86,45,2,123]seq.sort()print seq  #结果[2, 2, 12, 12, 14, 45, 86, 123, 123, 141]print search(seq,14)  #结果 4