python 写mapreduce

1.lambda
#?匿名函数
#?基本用法?lambda?x:?x**2
????#?第一个参数，然后是表达式
#?也可以使用如下
(lambda?x:?x**2)(5)2.?map()
def?map(function,?sequence,?*sequence_1):?#?real?signature?unknown;?restored?from?__doc__
????"""
????map(function,?sequence[,?sequence,?...])?->?list

????Return?a?list?of?the?results?of?applying?the?function?to?the?items?of
????the?argument?sequence(s).??If?more?than?one?sequence?is?given,?the
????function?is?called?with?an?argument?list?consisting?of?the?corresponding
????item?of?each?sequence,?substituting?None?for?missing?values?when?not?all
????sequences?have?the?same?length.??If?the?function?is?None,?return?a?list?of
????the?items?of?the?sequence?(or?a?list?of?tuples?if?more?than?one?sequence).
????"""
????return?[]

#?两个参数，一个处理函数，一个可迭代的序列
#?返回一个列表

#?例如?计算1到10的平方，并以列表的形式返回
map(lambda?x:?x**2,?range(1,?11))
#?结果如下
[1,?4,?9,?16,?25,?36,?49,?64,?81,?100]

#?当然?也可以如下这样使用
def?square(x):
????return?x**2

map(square,?range(1,?11))3.reduce()
def?reduce(function,?sequence,?initial=None):?#?real?signature?unknown;?restored?from?__doc__
????"""
????reduce(function,?sequence[,?initial])?->?value

????Apply?a?function?of?two?arguments?cumulatively?to?the?items?of?a?sequence,
????from?left?to?right,?so?as?to?reduce?the?sequence?to?a?single?value.
????For?example,?reduce(lambda?x,?y:?x+y,?[1,?2,?3,?4,?5])?calculates
????((((1+2)+3)+4)+5).??If?initial?is?present,?it?is?placed?before?the?items
????of?the?sequence?in?the?calculation,?and?serves?as?a?default?when?the
????sequence?is?empty.
????"""
????pass

#?两个参数，一个接受两个参数的函数，一个序列参数
#?例如?计算?1到10?的和
reduce(lambda?x,?y:?x+y,?range(1,?11))

#?当然，不适用lambda匿名函数也可以
def?add(x,?y):
????return?x+y
reduce(add,?range(1,?11))

#?结果如下
454.filter()
def?filter(function_or_none,?sequence):?#?known?special?case?of?filter
????"""
????filter(function?or?None,?sequence)?->?list,?tuple,?or?string

????Return?those?items?of?sequence?for?which?function(item)?is?true.??If
????function?is?None,?return?the?items?that?are?true.??If?sequence?is?a?tuple
????or?string,?return?the?same?type,?else?return?a?list.
????"""
????pass

#?接受两个参数，一个过滤函数，返回True?或者?False，?以及一个序列
#?例如，?计算100以内的偶数
filter(lambda?x:?x?%?2?==?0,?range(100))

#?如上
def?div2(x):
????if?x?%?2?==?0:
????????return?True
????else:
????????return?False
filter(div2,?range(100))

#?结果如下?
[0,?2,?4,?6,?8,?10,?12,?14,?16,?...?]