switch 语法结构：
switch 语句用于编写多分支结构的程序，类似于if...elif...eles语句。
swtch 语句的表达的分支结果比if...elif...lese 语句表达的更清晰，代码的可读性更高。
####python并没有提供switch语句######
但是：python 可以通过字典实现switch语句的功能。
实现方法：
定义一个字典
调用字典的get（）获取相应的表达式
范例：
>>> 6/4 1 >>> 6.0/4 1.5 >>> from __future__ import division >>> 5/2 2.5
# __future__模块 division 精确的除法
下面是一个计算器：
#!/usr/bin/python
#coding:utf-8
from __future__ import division
def jia(x,y):
return x+y
def jian(x,y):
return x-y
def chu(x,y):
return x/y
def cheng(x,y):
return x*y
def operator(x,o,y):
x =int(raw_input("plese somthing number:"))
y =int(raw_input("plese somthing number:"))
o = raw_input("plese somthing +/*-:")
if o == ‘+‘:
print jia(x,y)
elif o == ‘*‘:
print cheng(x,y)
elif o == ‘/‘:
print chu(x,y)
elif o == ‘-‘:
print jian(x,y)
else:
pass
print operator(‘x‘,‘o‘,‘y‘)
#注意三次判断是多余的，且如果符号错误，执行为空，效率不是很好
如果通过switch编写一个计算器
[[email protected] tools]# cat switch.py
#!/usr/bin/python
#coding:utf-8
from __future__ import division
def jia(x,y):
return x+y
def jian(x,y):
return x-y
def chu(x,y):
return x/y
def cheng(x,y):
return x*y
operator = {"+":jia,"-":jian,"*":cheng,"/":chu}
print jia(2,4)
print jia
print operator["+"](3,4) #通过字典取值，省去判断的环节；
[[email protected] tools]# python switch.py
6
<function jia at 0x7fc3ecb8fa28>
7
如果字典中没有值或值是错误的：print operator["（"](3,4)
报错如：Traceback (most recent call last):
File "switch.py", line 20, in <module>
print operator["("](3,4)
KeyError: ‘(‘
所以我们可以使用字典中get的方法：
Traceback (most recent call last): print operator.get["-"](3,4)
File "switch.py", line 21, in <module>
print operator.get["-"](3,4)
TypeError: ‘builtin_function_or_method‘ object is unsubscriptable
实现和if相同的操作：
[[email protected] tools]# cat switch.py
#!/usr/bin/python
#coding:utf-8
from __future__ import division
def jia(x,y):
return x+y
def jian(x,y):
return x-y
def chu(x,y):
return x/y
def cheng(x,y):
return x*y
operator = {"+":jia,"-":jian,"*":cheng,"/":chu}
def f(x,o,y):
print operator.get(o)(x,y) #将字典中的key带入函数中，类似如if的判断
f(2,"-",4)
[[email protected] tools]# python switch.py
-2
时间： 2024-11-07 10:27:59