Gregor Lingl wrote:
> Hi all of you,
>
> I've some Vector class, which is a subclass of tuple and which is
> working satisfactorily since long in different contexts. Now I've
> constructed objects with attributes of Vec-type, which I wanted to
> deepcopy. But that doesn't work, because I can't (deep)copy Vec-s:
>
> >>> from copy import deepcopy
> >>> class Vec(tuple):
> def __new__(cls, x, y):
> return tuple.__new__(cls, (x,y))
> def __abs__(self):
> return (self[0]**2+self[1]**2)**0.5
> ## more methods ...
>
>
> >>> a=Vec(3,4)
> >>> abs(a)
> 5.0
> >>> b = deepcopy(a)
>
> Traceback (most recent call last):
> File "<pyshell#13>", line 1, in -toplevel-
> b = deepcopy(a)
> File "C:\Python24\lib\copy.py", line 204, in deepcopy
> y = _reconstruct(x, rv, 1, memo)
> File "C:\Python24\lib\copy.py", line 336, in _reconstruct
> y = callable(*args)
> File "C:\Python24\lib\copy_reg.py", line 92, in __newobj__
> return cls.__new__(cls, *args)
> TypeError: __new__() takes exactly 3 arguments (2 given)
Apparently you need to define __getnewargs__() for your class. This works:
def __getnewargs__(self):
return (self[0], self[1])
__getnewargs__() is documented with the pickle module but it is used by
deepcopy() as well.
http://docs.python.org/lib/pickle-inst.html
Kent
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