Python开关案例 [英] Python switch case

问题描述

我试图在python上使用字典作为switch case，但是，参数似乎没有传递给被调用的函数，请帮忙:

I am trying to use dictionary as switch case on python, however, the parameter does not seem to be pass to the called function, please help:

def switchcase(num,cc):
    def fa(num):
        out= num*1.1;
    def fb(num):
        out= num*2.2;
    def fc(num):
        out= num*3.3;
    def fd(num):
        out= num*4.4;
    options = {
        "a":fa(num),
        "b":fb(num),
        "c":fc(num),
        "d":fd(num)
        } 
    out=0
    options[cc];
    return out
print switchcase(10,"a")

输出为0，我没弄清楚问题

the output is 0, I could not figure out the problem

推荐答案

问题是:

out=0
options[cc];
return out

基本上 -- 无论 options[cc] 给你什么，你都会返回 0 因为这是 out 的值.请注意，在各种fa、fb、...函数中设置out 不会不改变out 在调用者中.

Basically -- no matter what options[cc] gives you, you're going to return 0 because that's the value of out. Note that setting out in the various fa, fb, ... functions does not change the value of out in the caller.

您可能想要:

def switchcase(num,cc):
    def fa(num):
        return num*1.1;
    def fb(num):
        return num*2.2;
    def fc(num):
        return num*3.3;
    def fd(num):
        return num*4.4;
    options = {
        "a":fa(num),
        "b":fb(num),
        "c":fc(num),
        "d":fd(num)
        } 
    return options[cc];

另请注意，这在实践中效率极低.每次调用 switchcase 时，您都会创建 4 个函数(并分别调用).

Also note that this will be horribly inefficient in practice. You're creating 4 functions (and calling each) every time you call switchcase.

我猜您实际上想要创建一个预制的函数映射.然后你可以从地图中选择你真正想要的函数并用给定的数字调用它:

I'm guessing that you actually want to create a pre-made map of functions. Then you can pick up the function that you actually want from the map and call it with the given number:

def fa(num):
    return num*1.1

def fb(num):
    return num*2.2

def fc(num):
    return num*3.3

def fd(num):
    return num*4.4

OPTIONS = {
    "a":fa,
    "b":fb,
    "c":fc,
    "d":fd
} 

def switchcase(num,cc):
    return OPTIONS[cc](num)

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