我想實現一個符號類型,它跟蹤我們已有的符號(保存在_sym_table
),並返回它們(如果它們存在)否則新的。代碼:copy.deepcopy用自定義的__new __()方法在對象上引發TypeError
# -*- 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,當我打電話copy.deepcopy
這樣Symbol
實例的名單上,引發異常:
a = Symbol('a')
b = Symbol('b')
s = [a, b]
t = copy.deepcopy(s)
錯誤消息:
Traceback (most recent call last):
File "xxx.py", line 7, in <module>
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)
所以我的問題是:
- H我可以使用自定義的
__new__
方法對這些對象進行深層複製嗎? - 有關何時以及如何使用
copy.deepcopy
的建議?
非常感謝!