switch 語法結構:
switch 語句用於編寫多分支結構的程序,類似於if...elif...eles語句。
swtch 語句的表達的分支結果比if...elif...lese 語句表達的更清晰,代碼的可讀性更高。
####python並沒有提供switch語句######
但是:python 可以通過字典實現switch語句的功能。
實現方法:
定義一個字典
調用字典的get()獲取相應的表達式
範例:
>>> 6/4 1 >>> 6.0/4 1.5 >>> from __future__ import division >>> 5/2 2.5
# __future__模塊 division 精確的除法
下面是一個計算器:
#!/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')
#注意三次判斷是多餘的,且如果符號錯誤,執行爲空,效率不是很好
如果通過switch編寫一個計算器
[root@zabbix 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) #通過字典取值,省去判斷的環節; [root@zabbix tools]# python switch.py 6 <function jia at 0x7fc3ecb8fa28> 7 如果字典中沒有值或值是錯誤的:print operator["("](3,4) 報錯如:Traceback (most recent call last): File "switch.py", line 20, in <module> print operator["("](3,4) KeyError: '(' 所以我們可以使用字典中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
實現和if相同的操作:
[root@zabbix 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) #將字典中的key帶入函數中,類似如if的判斷
f(2,"-",4)
[root@zabbix tools]# python switch.py
-2