我想實(shí)現(xiàn)一個(gè)符號(hào)類型,它跟蹤我們已經(jīng)擁有的符號(hào)(保存在_sym_table中),如果它們存在則返回它們,否則創(chuàng)建新符號(hào).代碼：

# -*- coding: utf-8 -*-

_sym_table = {}

class Symbol(object):

def __new__(cls, sym):

if sym not in _sym_table:

return super().__new__(cls)

else:

return _sym_table[sym]

def __init__(self, sym):

self.sym = sym

_sym_table[sym] = self

def __str__(self):

return self.sym

def __cmp__(self, other):

return self is other

def __hash__(self):

return self.sym.__hash__()

但是當(dāng)我在這樣的Symbol實(shí)例列表上調(diào)用copy.deepcopy時(shí),會(huì)引發(fā)異常：

a = Symbol('a')

b = Symbol('b')

s = [a, b]

t = copy.deepcopy(s)

錯(cuò)誤消息：

Traceback (most recent call last):

File "xxx.py", line 7, in

t = copy.deepcopy(s)

File "/usr/lib/python3.2/copy.py", line 147, in deepcopy

y = copier(x, memo)

File "/usr/lib/python3.2/copy.py", line 209, in _deepcopy_list

y.append(deepcopy(a, memo))

File "/usr/lib/python3.2/copy.py", line 174, in deepcopy

y = _reconstruct(x, rv, 1, memo)

File "/usr/lib/python3.2/copy.py", line 285, in _reconstruct

y = callable(*args)

File "/usr/lib/python3.2/copyreg.py", line 88, in __newobj__

return cls.__new__(cls, *args)

TypeError: __new__() takes exactly 2 arguments (1 given)

所以我的問(wèn)題是：

>如何使用自定義的__new__方法對(duì)這些對(duì)象進(jìn)行深層復(fù)制？

>以及關(guān)于何時(shí)以及如何使用copy.deepcopy的任何建議？

非常感謝！

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