Python 词典替换 switch/case 中的失败

Question

我尝试在 Python 中实现 switch/case 机制。在阅读了几个网站和此处的问题后（例如 this one), I built the code below. But it behaves wrong, having what I understand to be - a fall-through, which can be even problematic to get，肯定不是默认的预期结果。

def something():
    print 'something'

def somethingElse():
    print 'something else'

def switch():
    cases = {
        0: something(),
        1: something(),
        2: something(),
        3: something(),
        4: something(),
        5: something()
        }

    cases.get(2, somethingElse())

switch()

（显然每个案例的相同开关只是为了示例）

当我运行它时，我希望 something() 只运行一次（因为我手动输入 2）。但是，控制台中的输出是：

something
something
something
something
something
something
something else

什么意思是运行6倍加上默认值运行。我不明白这段代码中的什么允许这样的失败？或者问题可能不同？

这里是 Python 2.7.12。

Answer 1

您的词典在创建案例时会调用每个函数。您的函数打印（副作用）而不是 return 字符串，因此您会看到所有打印到控制台的字符串。

相反，您的开关应该 return 一个函数，然后您可以调用该函数。

def something():
    print 'something'

def somethingElse():
    print 'something else'

def switch():
    cases = {
        0: something,
        1: something,
        2: something,
        3: something,
        4: something,
        5: something
        }

    # All of the values in `cases` are functions so it is safe
    # to call whatever `cases.get(...)` returns.
    cases.get(2, somethingElse)()

switch()

Answer 2

你需要return函数名然后调用它。像这样

def something():
    print ('something')

def somethingElse():
    print ('something else')

cases = {1: something, 2: something, 3:something, 4:something,5:something}
result = cases.get(2, somethingElse)()

~

Python 词典替换 switch/case 中的失败

Fall-through in Python dictionary replacement of switch/case

python

switch-statement

fall-through