如何在python3.3用 map filter reduce
在3.3里,如果直接使用map(), filter(), reduce(), 会出现
>>> def f(x): return x % 2 != 0 and x % 3 != 0
>>> filter(f, range(2, 25)) <</span>filter object at 0x0000000002C14908>
>>> def cube(x): return x*x*x
>>> map(cube, range(1, 11)) <</span>map object at 0x0000000002C82B70> >>> defadd(x,y): return x+y
>>> reduce(add, range(1, 11)) Traceback (most recent call last): File "", line 1, in<</span>module> reduce(add, range(1, 11)) NameError: name 'reduce' is not defined
这种情况是因为在3.3里面,map(),filter()这些的返回值已经不再是list,而是iterators, 所以想要使用,只用将iterator 转换成list 即可, 比如 list(map())
而reduce已经取消了,如想使用,可以用fuctools.reduce来调用。但是要先导入fuctools, 即输入:import fuctools
e.g1
>>>
sentence = 'It is raining cats and dogs'
>>>
words = sentence.split()
>>>
print words
['It', 'is', 'raining', 'cats', 'and', 'dogs'] |
>>>
>>>
lengths = map(lambda word: len(word), words)
>>>
print (list(lengths))
[2, 2, 7, 4, 3, 4]
e.g2
>>> import functools
>>> def add(x,y): return x+y ...
>>> functools.reduce(add, range(1, 11)) 55