这里有很多问题。第一个是 IPython(Jupyter 在幕后使用的东西,当您看到类似的内容时,会保留对对象的附加引用)Out[67]
。事实上,您可以使用该语法来调用该对象并对其执行某些操作。例如。str(Out[67])
。第二个问题是 Jupyter 似乎保留了自己的输出变量引用,因此只有完全重置 IPython 才有效。但这与重新启动笔记本电脑没有太大区别。
不过有一个解决方案!我编写了一个您可以运行的函数,该函数将清除所有变量,除了您明确要求保留的变量之外。
def my_reset(*varnames):
"""
varnames are what you want to keep
"""
globals_ = globals()
to_save = {v: globals_[v] for v in varnames}
to_save['my_reset'] = my_reset # lets keep this function by default
del globals_
get_ipython().magic("reset")
globals().update(to_save)
你会像这样使用它:
x = 1
y = 2
my_reset('x')
assert 'y' not in globals()
assert x == 1
下面我写了一个笔记本,向您展示了幕后发生的一些事情,以及如何使用weakref
模块。您可以尝试运行它,看看它是否可以帮助您了解发生了什么。
In [1]: class MyObject:
pass
In [2]: obj = MyObject()
In [3]: # now lets try deleting the object
# First, create a weak reference to obj, so we can know when it is truly deleted.
from weakref import ref
from sys import getrefcount
r = ref(obj)
print("the weak reference looks like", r)
print("it has a reference count of", getrefcount(r()))
# this prints a ref count of 2 (1 for obj and 1 because getrefcount
# had a reference to obj)
del obj
# since obj was the only strong reference to the object, it should have been
# garbage collected now.
print("the weak reference looks like", r)
the weak reference looks like <weakref at 0x7f29a809d638; to 'MyObject' at 0x7f29a810cf60>
it has a reference count of 2
the weak reference looks like <weakref at 0x7f29a809d638; dead>
In [4]: # lets try again, but this time we won't print obj, will just do "obj"
obj = MyObject()
In [5]: print(getrefcount(obj))
obj
2
Out[5]: <__main__.MyObject at 0x7f29a80a0c18>
In [6]: # note the "Out[5]". This is a second reference to our object
# and will keep it alive if we delete obj
r = ref(obj)
del obj
print("the weak reference looks like", r)
print("with a reference count of:", getrefcount(r()))
the weak reference looks like <weakref at 0x7f29a809db88; to 'MyObject' at 0x7f29a80a0c18>
with a reference count of: 7
In [7]: # So what happened? It's that Out[5] that is keeping the object alive.
# if we clear our Out variables it should go away...
# As it turns out Juypter keeps a number of its own variables lying around,
# so we have to reset pretty everything.
In [8]: def my_reset(*varnames):
"""
varnames are what you want to keep
"""
globals_ = globals()
to_save = {v: globals_[v] for v in varnames}
to_save['my_reset'] = my_reset # lets keep this function by default
del globals_
get_ipython().magic("reset")
globals().update(to_save)
my_reset('r') # clear everything except our weak reference to the object
# you would use this to keep "thing" around.
Once deleted, variables cannot be recovered. Proceed (y/[n])? y
In [9]: print("the weak reference looks like", r)
the weak reference looks like <weakref at 0x7f29a809db88; dead>