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python中有switch语句吗
为什么Python中没有Switch/Case语句
[Python里怎么实现switch case](#Python里怎么实现switch case)
如何理解 python中的switch

python中有switch语句吗

python官网的回答（地址：）： You can do this easily enough with a sequence of if... elif... elif... else. 意思就是：python语法讲究简单明了，if else完全可以很简单的实现switch的所有功能，没必要用switch。

为什么Python中没有Switch/Case语句

因为作为一门解释型语言，switch/case是没有存在必要的，if/elif/else就可以实现的功能，为什么要再提供重复的？ if else的得一个if一个if的判断过去，如果匹配的是最后一个条件，前面所有if都得判断一遍的。看过汇编就知道，C语言的switch/case，在case值连续的时候，是可以根据case值直接计算该跳转的地址的。

Python里怎么实现switch case

学习Python过程中，发现没有switch-case,过去写C习惯用Switch/Case语句，官方文档说通过if-elif实现。所以不妨自己来实现Switch/Case功能。

方法一

通过字典实现

def foo(var):
    return {
        'a': 1,
        'b': 2,
        'c': 3,
    }.get(var, 'error')  # 'error'为默认返回值，可自设置

方法二

通过匿名函数实现

def foo(var, x):
    return {
        'a': lambda x: x + 1,
        'b': lambda x: x + 2,
        'c': lambda x: x + 3,
    }[var](x)

方法三

通过定义类实现参考Brian Beck通过类来实现Swich-case

# 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
# break is used here to look as much like the real thing as possible, but
# elif is generally just as good and more concise.
# Empty suites are considered syntax errors, so intentional fall-throughs
# should contain 'pass'
c = 'z'
for case in switch(c):
    if case('a'):
        pass  # only necessary if the rest of the suite is empty
    if case('b'):
        pass
    # ...
    if case('y'):
        pass
    if case('z'):
        print("c is lowercase!")
        break
    if case('A'):
        pass
    # ...
    if case('Z'):
        print("c is uppercase!")
        break
    if case():  # default
        print("I dunno what c was!")
# As suggested by Pierre Quentel, you can even expand upon the
# functionality of the classic 'case' statement by matching multiple
# cases in a single shot. This greatly benefits operations such as the
# uppercase/lowercase example above:
import string
c = 'A'
for case in switch(c):
    if case(*string.lowercase):  # note the * for unpacking as arguments
        print("c is lowercase!")
        break
    if case(*string.uppercase):
        print("c is uppercase!")
        break
    if case('!', '?', '.'):  # normal argument passing style also applies
        print("c is a sentence terminator!")
        break
    if case():  # default
        print("I dunno what c was!")
# Since Pierre's suggestion is backward-compatible with the original recipe,
# I have made the necessary modification to allow for the above usage.

查看Python官方: PEP 3103 - A Switch/Case Statement 发现其实实现Switch Case需要被判断的变量是可哈希的和可比较的，这与Python倡导的灵活性有冲突。在实现上，优化不好做，可能到最后最差的情况汇编出来跟If Else组是一样的。所以Python没有支持。

如何理解 python中的switch

方法/步骤

我们以加减和一个随意名字的函数来解析switch的用法，说白了也是很简答吗的。首先添加一个add的方法。
再添加一个相减的方法，同时加了print方便debug程序。
之后为了作对比，随便写了一个abc的方法。
建立一个字典，用‘+’，‘-’，‘abc’分别作为key，对应相映的方法。
之后再加两个方法，通过对于参数的调整，用字典的get‘key’方法获取函数，并且传入参数。
试着用（1，‘+’，5）来实现1+5。
用（6，‘-’，2）来实现6-2，调用的都是同一个方法，参数不同，通过字典key获取到的函数也不同，这就是我所理解的switch的用法。
最后，随便试一下，用‘abc’也可以，哈哈。

包含python之switch语句的词条