推 xinu:Thanks..又學到了新招~ 08/06 23:25
※ 引述《xinu (xinu)》之銘言：
: 請問一下在python裡
: 有辦法藉由class裡的某個member(attribute)
: 就找到該Class嗎?
: 假設c裡面是這樣寫的話
: struct A {
: ....
: ....
: int a; //certain member
: };
: struct A a;
: void *ptr = &a.a;
: ptr= ptr - ((struct A *)0)->a;
: ptr這時候會等於 &a;
: 這樣子的暴力手段python有辦法實作出來嗎?
: 或是有什麼其他替代方案? 我看introspection裡好像沒提到這段...
python object 裡的 attr 都是 reference ,
所以有可能多個 object 的某 attr 都指向同一個 reference .
這一點與 C 有很大的不同.
硬要做到這種功能不是不行，底下是用間接的方法列舉 object 來找.
因為我找不到 python 有類似 ruby 的 ObjectSpace 功能，所以自己做一個.
import weakref
ObjectSpace = {}
class OSObject:
@classmethod
def contain_of(cls, target, attr):
os_cls = ObjectSpace.setdefault(cls, [])
# # clean up invalid objects
# os_cls[:] = [ obj for obj in os_cls if obj() ]
objs = [obj() for obj in os_cls
if obj() and target is getattr(obj(), attr) ]
return objs
def os_store(self):
cls = self.__class__
os_cls = ObjectSpace.setdefault(cls, [])
os_cls.append(weakref.ref(self))
def __init__(self, array):
self.os_store()
self.array = array
if __name__ == '__main__':
target1 = [1, 2, 3]
target2 = [4, 5, 6]
target3 = [7, 8, 9]
a = OSObject(target1)
b = OSObject(target2)
c = OSObject(target1)
print "object a: ", a
print "object b: ", b
print "object c: ", c
print "find objects which contain target1 as attribute 'array'"
print OSObject.contain_of(target1, "array")
print "find objects which contain target2 as attribute 'array'"
print OSObject.contain_of(target2, "array")
print "find objects which contain target3 as attribute 'array'"
print OSObject.contain_of(target3, "array")
result:
object a: <__main__.OSObject instance at 0x81b1d4c>
object b: <__main__.OSObject instance at 0x81bcd8c>
object c: <__main__.OSObject instance at 0x81bcdac>
find objects which contain target1 as attribute 'array'
[<__main__.OSObject instance at 0x81b1d4c>, # a
<__main__.OSObject instance at 0x81bcdac>] # c
find objects which contain target2 as attribute 'array'
[<__main__.OSObject instance at 0x81bcd8c>] # b
find objects which contain target3 as attribute 'array'
[] # None
--
※ 發信站: 批踢踢實業坊(ptt.cc)
◆ From: 140.113.23.204