本文目录一览：
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
1
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。
2
再添加一个相减的方法，同时加了print方便debug程序。
3
之后为了作对比，随便写了一个abc的方法。
4
建立一个字典，用‘+’，‘-’，‘abc’分别作为key，对应相映的方法。
5
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。
6
试着用（1，‘+’，5） 来实现1+5。
7
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。
8
最后，随便试一下，用‘abc’也可以，哈哈。