Python编程实例（4）

1.partial函数的使用

functools.partial 通过包装手法，允许我们 “重新定义” 函数签名1.

例：

给两条形如

y=m*x+b

的直线，给定起点

l

和终点

r

取他们之间的整数作为输入判断y值的大小并计数，若

y1>y2

的点多，则输出为

first

,若

y1<y2

的点多，则输出为

second

，若一样多则输出为

any

。

For line1 = [1, 2], line2 = [2, 1], l = 0 and r = 2, the output should be
twoLines(line1, line2, l, r) = "any";

For line1 = [1, 2], line2 = [2, 1], l = -1 and r = 2, the output should be
twoLines(line1, line2, l, r) = "first";

For line1 = [1, 2], line2 = [2, 1], l = 0 and r = 3, the output should be
twoLines(line1, line2, l, r) = "second"

示例代码如下：

from functools import partial

def line_y(m, b, x):
return m * x + b

def twoLines(line1, line2, l, r):
line1_y = partial(line_y,line1[0],line1[1])
line2_y = partial(line_y,line2[0],line2[1])
balance = 0
for x in range(l, r + 1):
y1 = line1_y(x)
y2 = line2_y(x)
if y1 > y2:
balance += 1
elif y1 < y2:
balance -= 1
if balance > 0:
return "first"
if balance < 0:
return "second"
return "any"

2.函数的组合使用

例如：

f = "math.log10", g = "abs" and x = -100

则输出为：

simpleComposition(f, g, x) = 2

示例代码：

def compose(f, g):
return lambda x:f(g(x))

def simpleComposition(f, g, x):
return compose(eval(f), eval(g))(x)

3.函数列表重新组成新的函数

Input:
functions = ["abs", "math.sin", "lambda x: 3 * x / 2"]
x = 3.1415
Output:
functionsComposition(functions, x) = 1

示例代码如下：

def compose(functions):
return reduce(lambda f, g: lambda x: f(g(x)), functions)

def functionsComposition(functions, x):
return compose(map(eval, functions))(x)

4.Python中装饰器的使用

对列表第

2*i-1

和

2*i

个数求和，

i

从1开始。

示例：

Input
vines = [1, 2, 3, 4, 5] and n = 2
Output:
mergingVines(vines, n) = [10, 5]
1 :[1+2,3+4,5]
2 :[3+7,5]=[10,5]

示例代码：

def mergingVines(vines, n):
def nTimes(n):
def apply_n_times(f):
if n == 0:
return lambda x: x
else:
return lambda x: f(nTimes(n - 1)(f)(x))
return apply_n_times

@nTimes(n)
def sumOnce(vines):
res = [vines[i] + vines[i + 1] for i in range(0, len(vines) - 1, 2)]
if len(vines) % 2 == 1:
res.append(vines[-1])
return res

return sumOnce(vines)

主要是

python

中代参数装饰器的使用2.

Refer

1 http://www.wklken.me/posts/2013/08/18/python-extra-functools.html

2 http://gohom.win/2015/10/25/pyDecorator/