python的几个内建函数:apply(),filter(),map(),reduce()

apply()函数: apply(func[,nkw][,kw]) 它的返回值就是func函数的返回值

filter()函数:  filter(func,seq) 调用bool函数func，遍历处理序列中seq的每个元素。它的返回值是一个序列，其元素都是让func函数返回true值的原seq序列中的元素

map()函数:

def map(func,seq):

    mapped_seq = []

    for eachItem in seq:

        mapped_seq.append(apply(func,eachItem))

    return mapped_seq

reduce()函数:reduce(func,seq[,init]),用二元函数func对序列seq中的元素进行处理，每次处理两个数据项(一个是前次处理的结果，一个是序列中的下一个元素)，如此反复的递归处理，最后对整个序列求出一个单一的返回值。

1.apply()函数

 1.1 apply()函数对于调用那些参数是动态生成的函数是非常方便的，一般牵扯到拼凑一个参数清单这种问题

matheasy.py

#!/usr/bin/env/ python

from string import lower

from operator import add,sub,mul

from random import randint,choice

ops = {'+':add,'-':sub,'*':mul}

MAXTRIES = 2

def doprob():

    op = choice('+-*')

    nums = [randint(1,10),randint(1,10)]

    nums.sort();nums.reverse()

    ans = apply(ops[op],nums)

    pr = '%d %s %d = ' %( nums[0],op,nums[1])

    oops = 0

    while 1:

        try:

            if int(raw_input(pr)) == ans:

                print "correct"

                break

            if oops == MAXTRIES:

                print 'answer/n%s%d' %(pr,ans)

                break

            else:

                print 'incorrect ... try again'

                oops = oops + 1

        except(KeyboardInterrupt,EOFError,ValueError):

            print 'invalid input data ... try again'

            

def main():

    print 'welcome to play this game:'

    while 1:

        doprob()

        try:

            opt = lower(raw_input('Try again? ([y]/n)'))

        except(KeyboardInterrupt,EOFError):

            print ;break

        if opt and opt[0] =='n':

            print 'quit the game,byebye'

            break

if __name__ == '__main__':

    main()

            

        

        

        

        

        

 1.2 apply()函数对于应用程序的调试纠错和性能测试方面也是很有用的。一般是编写一个诊断性函数来建立测试环境，然后调用准备对它进行测试的函数，考虑到系统的灵活性和适应性，被测试函数作为一个参数传递进去

testit.py

#!/usr/bin/env/ python

def testit(funcname,*nkwargs,**kwargs):

    try:

        retval = apply(funcname,nkwargs,kwargs)

        result = (1,retval)

    except Exception,diag:

        result = (0,str(diag))

    return result

def test():

    funcs = (int,long,float)

    vals = (1234,12.34,'1234','12.34')

    

    for eachFunc in funcs:

        print '-'*40

        for eachVal in vals:

            retval = testit(eachFunc,eachVal)

            

            if retval[0]:

                print '%s(%s) = ' %(eachFunc.__name__,eachVal),retval[1]

            else:

                print '%s(%s) = FAILED ' %(eachFunc.__name__,eachVal),retval[1]

                

if __name__ == '__main__':

    test()

       

2.filter()函数

oddnumgen.py

from random import randint

def odd():

    allNums = []

    for eachNum in range(100):

        allNums.append(randint(1,1000))

    oddNums = filter(lambda n:n%2,allNums)

    print "length of sequence = %d/n" %(len(oddNums)),oddNums

3.map()函数

>>>map(lambda x,y:(x+y,x-y),[1,3,5],[2,4,6])

>>> [(3, -1), (7, -1), (11, -1)]

from string import strip,upper

def strupper():

    f = open('map.txt')

    lines = f.readlines()

    f.close() 

    print ' ... BEFORE processing ...'

    for eachLine in lines:

        print '<%s>' %eachLine[:-1]#去掉换行符

    print "/n" 

    print ' ... AFTER processing ...'    

    for eachLine in map(upper,map(strip,lines)):#strip不清理字符串之间的空格

        print '<%s>' %eachLine

 

def rounder():

    f = open('round.txt')              

    values = map(float,f.readlines()) 

    f.close() 

    

    print 'original/trounded'

    for eachVal in map(None,values,map(round,values)):#函数为None,那么参数列表中的n个序列(此时为values和map(round,values) )组成了返回值的列表

        print '%6.02f/t/t%6.02f' %eachVal

4.reduce()函数

 >>> print 'the total is:',total = reduce((lambda x,y:x+y),range(1000))