python的幾個內建函數:apply(),filter(),map(),reduce()
apply()函數: apply(func[,nkw][,kw]) 它的返回值就是func函數的返回值
filter()函數: filter(func,seq) 調用bool函數func，遍歷處理序列中seq的每個元素。它的返回值是一個序列，其元素都是讓func函數返回true值的原seq序列中的元素
map()函數:
def map(func,seq):
mapped_seq = []
for eachItem in seq:
mapped_seq.append(apply(func,eachItem))
return mapped_seq
reduce()函數:reduce(func,seq[,init]),用二元函數func對序列seq中的元素進行處理，每次處理兩個數據項(一個是前次處理的結果，一個是序列中的下一個元素)，如此反覆的遞歸處理，最後對整個序列求出一個單一的返回值。
1.apply()函數
1.1 apply()函數對於調用那些參數是動態生成的函數是非常方便的，一般牽扯到拼湊一個參數清單這種問題
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()函數對於應用程序的調試糾錯和性能測試方面也是很有用的。一般是編寫一個診斷性函數來建立測試環境，然後調用準備對它進行測試的函數，考慮到系統的靈活性和適應性，被測試函數作爲一個參數傳遞進去
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()函數
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()函數
>>>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]#去掉換行符
print "/n"
print ' ... AFTER processing ...'
for eachLine in map(upper,map(strip,lines)):#strip不清理字符串之間的空格
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)):#函數爲None,那麼參數列表中的n個序列(此時爲values和map(round,values) )組成了返回值的列表
print '%6.02f/t/t%6.02f' %eachVal
4.reduce()函數
>>> print 'the total is:',total = reduce((lambda x,y:x+y),range(1000))