我很好奇python中__del__
的细节,什么时候应该用,为什么用,什么不应该用。我学到了一个艰难的方法,它并不像人们天真地期望从析构函数中得到的那样,因为它不是 __new__
/__init__
的对立面。
class Foo(object):
def __init__(self):
self.bar = None
def open(self):
if self.bar != 'open':
print 'opening the bar'
self.bar = 'open'
def close(self):
if self.bar != 'closed':
print 'closing the bar'
self.bar = 'close'
def __del__(self):
self.close()
if __name__ == '__main__':
foo = Foo()
foo.open()
del foo
import gc
gc.collect()
我在文档中看到 不 保证 __del__()
方法会在解释器退出时仍然存在的对象调用。
- 如何保证解释器退出时存在的任何
Foo
实例都关闭栏? - 在上面的代码片段中,栏是在
del foo
或gc.collect()
... 上关闭的,还是两者都没有?如果您想更好地控制这些细节(例如,当对象未被引用时应该关闭栏)通常的实现方法是什么? - 当
__del__
被调用时,是否保证__init__
已经被调用?如果__init__
提出了怎么办?
最佳答案
关闭资源的方法是上下文管理器,也就是 with
语句:
class Foo(object):
def __init__(self):
self.bar = None
def __enter__(self):
if self.bar != 'open':
print 'opening the bar'
self.bar = 'open'
return self # this is bound to the `as` part
def close(self):
if self.bar != 'closed':
print 'closing the bar'
self.bar = 'close'
def __exit__(self, *err):
self.close()
if __name__ == '__main__':
with Foo() as foo:
print foo, foo.bar
输出:
opening the bar
<__main__.Foo object at 0x17079d0> open
closing the bar
2) Python 的对象在引用计数为 0 时被删除。在您的示例中,del foo
删除了最后一个引用,因此立即调用了 __del__
。 GC 与此无关。
class Foo(object):
def __del__(self):
print "deling", self
if __name__ == '__main__':
import gc
gc.disable() # no gc
f = Foo()
print "before"
del f # f gets deleted right away
print "after"
输出:
before
deling <__main__.Foo object at 0xc49690>
after
gc
与删除您和大多数其他对象无关。当简单的引用计数由于自引用或循环引用而不起作用时,它可以清理:
class Foo(object):
def __init__(self, other=None):
# make a circular reference
self.link = other
if other is not None:
other.link = self
def __del__(self):
print "deling", self
if __name__ == '__main__':
import gc
gc.disable()
f = Foo(Foo())
print "before"
del f # nothing gets deleted here
print "after"
gc.collect()
print gc.garbage # The GC knows the two Foos are garbage, but won't delete
# them because they have a __del__ method
print "after gc"
# break up the cycle and delete the reference from gc.garbage
del gc.garbage[0].link, gc.garbage[:]
print "done"
输出:
before
after
[<__main__.Foo object at 0x22ed8d0>, <__main__.Foo object at 0x22ed950>]
after gc
deling <__main__.Foo object at 0x22ed950>
deling <__main__.Foo object at 0x22ed8d0>
done
3) 让我们看看:
class Foo(object):
def __init__(self):
raise Exception
def __del__(self):
print "deling", self
if __name__ == '__main__':
f = Foo()
给予:
Traceback (most recent call last):
File "asd.py", line 10, in <module>
f = Foo()
File "asd.py", line 4, in __init__
raise Exception
Exception
deling <__main__.Foo object at 0xa3a910>
对象是用 __new__
创建的,然后作为 self
传递给 __init__
。在 __init__
中出现异常后,该对象通常没有名称(即 f =
部分未运行),因此它们的引用计数为 0。这意味着对象被正常删除并调用__del__
。
关于python - 如何强制删除python对象?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/6772481/