filter,map,reduce,lambda（python3）

1.filter

filter（function,sequence）

对sequence中的item依次执行function（item），将执行的结果为True（符合函数判断）的item组成一个list、string、tuple（根据sequence类型决定）返回。

 #!/usr/bin/env python
 # encoding: utf-8
 """
 @author: 侠之大者kamil
 @file: filter.py
 @time: 2016/4/9 22:03
 """
 #filter map reduce lambda
 def f1(x):
     return x % 2 != 0 and x % 3 != 0
 a = filter(f1, range(2,25))
 print(a)#<filter object at 0x7f7ee44823c8>
 #这种情况是因为在3.3里面，filter()的返回值已经不再是list,而是iterators.
 print(list(a))
 def f2(x):
     return x != "a"
 print(list(filter(f2,"dfsafdrea")))

结果：

ssh://kamil@192.168.16.128:22/usr/bin/python3 -u /home/kamil/py22/jiqiao0406/fmrl.py
<filter object at 0x7f4d1ca5e470>
[5, 7, 11, 13, 17, 19, 23]
['d', 'f', 's', 'f', 'd', 'r', 'e']
 
Process finished with exit code 0

2.map

语法与filter类似

 #!/usr/bin/env python
 # encoding: utf-8
 """
 @author: 侠之大者kamil
 @file: map.py
 @time: 2016/4/9 22:22
 """
 def cube(x):
     return x * x *x
 a = map(cube,range(10))
 print(list(a))
 def add(x,y,z):
     return x + y +z
 b = map(add,range(5),range(5),range(5))
 print(list(b))

结果：

ssh://kamil@192.168.16.128:22/usr/bin/python3 -u /home/kamil/py22/jiqiao0406/map.py
[0, 1, 8, 27, 64, 125, 216, 343, 512, 729]
[0, 3, 6, 9, 12]
 
Process finished with exit code 0

3.reduce

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

4.lambda

快速定义最小单行函数

 g = lambda x:x *2
 print(g(5))
 print((lambda x:x *2)(5))

结果：

10
10