如何强制删除Python对象？

我很好奇的细节__del__在 python 中，何时、为什么应该使用它以及不应该使用它。我经历了惨痛的教训才知道，它并不像人们天真地期望的析构函数那样，因为它并不是与__new__ / __init__.

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()

我在文档中看到它是not保证__del__()为解释器退出时仍然存在的对象调用方法。

1. 如何保证对于任意Foo当解释器退出时存在实例，酒吧关闭吗？
2. 在上面的代码片段中，栏是否关闭del foo or on gc.collect()...或者两者都不是？如果您想要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？
3. when __del__被称为是否保证__init__已经被调用了？如果__init__ raised?

关闭资源的方法是上下文管理器，又名with陈述：

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

output:

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。在你的例子中del foo删除最后一个引用，所以__del__立即被调用。 GC 不参与此事。

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"

output:

before
deling <__main__.Foo object at 0xc49690>
after

The 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，它可以进行清理：

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"

output:

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()

gives:

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>

对象是用创建的__new__然后传递给__init__ as self。发生异常后__init__，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。这意味着该对象被正常删除并且__del__叫做。