[转载] Python没有switch语句的解决方法

from http://i.azpala.com/2008/01/20/python-switch/

其他语言中，switch语句大概是这样的

switch (var)
{
    case value1: do_some_stuff1();
    case value2: do_some_stuff2();
    ...
    case valueN: do_some_stuffN();
    default: do_default_stuff();
}

而python本身没有switch语句，解决方法有以下3种:

A.使用dictionary

values = {
           value1: do_some_stuff1,
           value2: do_some_stuff2,
           ...
           valueN: do_some_stuffN,
         }
values.get(var, do_default_stuff)()

具体请参考: Python switch statement

这个方法的缺点是:我不知道do_some_stuff是不是允许多个语句，如何实现，

也许是可以的，我不知道-.-

B.使用lambda

在PHP中，

switch ($value) {
    case 'a':
       $result = $x * 5;
        break;
    case 'b':
        $result = $x + 7;
        break;
    case 'c':
        $result = $x - 2;
        break;
}

在python中:

result = {
 'a': lambda x: x * 5,
 'b': lambda x: x + 7,
 'c': lambda x: x - 2
}[value](x)

具体参考: Switch statements in Python

C.Brian Beck提供了一个类 switch 来实现其他语言中switch的功能

# This class provides the functionality we want. You only need to look at
# this if you want to know how this works. It only needs to be defined
# once, no need to muck around with its internals.
class switch(object):
    def __init__(self, value):
        self.value = value
        self.fall = False
 
    def __iter__(self):
        """Return the match method once, then stop"""
        yield self.match
        raise StopIteration
 
    def match(self, *args):
        """Indicate whether or not to enter a case suite"""
        if self.fall or not args:
            return True
        elif self.value in args: # changed for v1.5, see below
            self.fall = True
            return True
        else:
            return False
 
# The following example is pretty much the exact use-case of a dictionary,
# but is included for its simplicity. Note that you can include statements
# in each suite.
v = 'ten'
for case in switch(v):
    if case('one'):
        print 1
        break
    if case('two'):
        print 2
        break
    if case('ten'):
        print 10
        break
    if case('eleven'):
        print 11
        break
    if case(): # default, could also just omit condition or 'if True'
        print "something else!"
        # No need to break here, it'll stop anyway