<p>首先考虑<a href="http://effbot.org/pyfaq/why-isn-t-there-a-switch-or-case-statement-in-python.htm" rel="noreferrer">why there is no case statement in Python</a>。所以让你的大脑复位,忘掉它们。</p>
<p>可以使用对象类、函数装饰器或函数字典来获得相同或更好的结果。</p>
<p>下面是一个简单的例子:</p>
<pre><code>#!/usr/bin/env python
import re
def hat(found):
if found: print "found a hat"
else: print "no hat"
def cat(found):
if found: print "found a cat"
else: print "no cat"
def dog(found):
if found: print "found a dog"
else: print "no dog"
st="""
Here is the target string
with a hat and a cat
no d o g
end
"""
patterns=['hat', 'cat', 'dog']
functions=[hat,cat,dog]
for pattern,case in zip(patterns,functions):
print "pattern=",pattern
case(re.search(pattern,st))
</code></pre>
<p>C样式的case/switch语句也“失败”,例如:</p>
<pre><code> switch(c) {
case 'a':
case 'b':
case 'c': do_abc();
break;
... other cases...
}
</code></pre>
<p>使用元组和可调用列表,可以获得类似的行为:</p>
<pre><code>st="rat kitten snake puppy bug child"
def proc1(st): print "cuddle the %s" % st
def proc2(st): print "kill the %s" % st
def proc3(st): print "pick-up the %s" % st
def proc4(st): print "wear the %s" % st
def proc5(st): print "dispose of the %s" %st
def default(st): print "%s not found" % st
dproc={ ('puppy','kitten','child'):
[proc3, proc1],
('hat','gloves'):
[proc3, proc4],
('rat','snake','bug'):
[proc2, proc3, proc5]}
for patterns,cases in dproc.iteritems():
for pattern in patterns:
if re.search(pattern,st):
for case in cases: case(pattern)
else: default(pattern)
print
</code></pre>
<p>这得到了找到的物品的正确顺序:1)抱起孩子,拥抱孩子;2)杀死老鼠,抱起老鼠。。。用可理解的语法对C switch语句执行同样的操作是很困难的。</p>
<p>还有很多其他方法可以模拟C开关语句。这里有一个(用于整数)使用函数装饰符:</p>
<pre><code>case = {}
def switch_on(*values):
def case_func(f):
case.update((v, f) for v in values)
return f
return case_func
@switch_on(0, 3, 5)
def case_a(): print "case A"
@switch_on(1,2,4)
def case_b(): print "case B"
def default(): print "default"
for i in (0,2,3,5,22):
print "Case: %i" % i
try:
case[i]()
except KeyError:
default()
</code></pre>
<p>套用Larry Wall、Tom Christiansen、Jon Orwant在<a href="http://www.perlmonks.org/?node_id=738558" rel="noreferrer">Programming Perl</a>中关于理解Perl中的上下文的话:</p>
<blockquote>
<p>You will be miserable programming Python until you use the idioms that are native to the language...</p>
</blockquote>