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Your task is to write a higher order function for chaining together a list of unary functions. In other words, it should return a function that does a left fold on the given functions.
chained([a,b,c,d])(input)
Should yield the same result as
d(c(b(a(input))))
返回值是由原参数构成的函数，解析成多层函数的嵌套。input 是内层的参数。
1 def chained(functions): 2 def apply(param): 3 result = param 4 for f in functions: 5 result = f(result) 6 return result 7 return apply
param 可是换成 result, 省略第三行（如下），不过不省略会语义上更清晰易读。注意 result 的作用域，别写成 for 的局部变量了
完整可运行代码如下：
1 #!/usr/bin/python 2 # -*- coding: utf-8 -*- 3 4 __author__ = ‘pudding‘ 5 6 7 def chained(functions): 8 def apply(result): 9 for f in functions: 10 result = f(result) 11 return result 12 return apply 13 14 15 def f1(x): return x*2 16 17 18 def f2(x): return x+2 19 20 21 def f3(x): return x**2 22 23 def f4(x): return x.split() 24 25 26 def f5(xs): return [x[::-1].title() for x in xs] 27 28 29 def f6(xs): return "_".join(xs) 30 31 32 if __name__ == ‘__main__‘: 33 print chained([f1, f2, f3])(0)
输出结果：4 即：((0**2)+2)*2
apply一开始的参数（result 的初始值）为 chained([f1, f2, f3])(0)中的0
【codewar】Unary function chainer
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原文地址：http://www.cnblogs.com/pudding-ai/p/5820254.html
