Python中為什麼沒有switch語法結構，有什麼代替方案嗎？

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

if __name__ == "__main__":

# 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, itll 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!"