python 自定义序列

def checkIndex(key):

if key < 0: raise IndexError

if not isinstance(key, (int , long)): raise TypeError

class NumberQueue:

def __init__(self, start=0, step=1):

self.start = start

self.step = step

self.change = {}

def __getitem__(self, key):

checkIndex(key)

try: return self.change[key]

except:

return self.start + key * self.step

def __setitem__(self, key, value):

checkIndex(key)

self.change[key] = value

nq1 = NumberQueue(1,1)

print nq1[4]

nq1[4]=2

print nq1[4]