Python 删除列表中的所有对象

Delete all objects in a list

提问by Jean-Francois Gallant

I create many object then I store in a list. But I want to delete them after some time because I create news one and don't want my memory goes high (in my case, it jumps to 20 gigs of ram if I don't delete it).

我创建了许多对象，然后存储在一个列表中。但我想在一段时间后删除它们，因为我创建了一个新闻并且不希望我的记忆变高（在我的情况下，如果我不删除它，它会跳到 20 gigs 的内存）。

Here is a little code to illustrate what I trying to do:

这是一个小代码来说明我尝试做的事情：

class test:
    def __init__(self):
        self.a = "Hello World"
    def kill(self):
        del self

a = test()
b = test()
c = [a,b]

print("1)Before:",a,b)

for i in c:
    del i

for i in c:
    i.kill()   

print("2)After:",a,b)

A and B are my objects. C is a list of these two objects. I'm trying to delete it definitely with a for-loop in C: one time with DEL and other time with a function. It's not seem to work because the print continue to show the objects.

A 和 B 是我的对象。C 是这两个对象的列表。我正在尝试使用 C 中的 for 循环绝对删除它：一次使用 DEL，另一次使用函数。它似乎不起作用，因为打印继续显示对象。

I need this because I create 100 000 objects many times. The first time I create 100k object, the second time another 100k but I don't need to keep the previous 100k. If I don't delete them, the memory usage goes really high, very quickly.

我需要这个，因为我多次创建 100 000 个对象。我第一次创建 100k 对象，第二次再创建 100k 但我不需要保留之前的 100k。如果我不删除它们，内存使用率会非常高，非常快。

采纳答案by mgilson

tl;dr;

tl;博士;

mylist.clear()  # Added in python3.(? maybe 5?)
del mylist[:]

are probably the best ways to do this. The rest of this answer tries to explain why some of your other efforts didn't work.

可能是最好的方法来做到这一点。这个答案的其余部分试图解释为什么你的其他一些努力没有奏效。

---

---

cpython at least works on reference counting to determine when objects will be deleted. Here you have multiple references to the same objects. arefers to the same object that c[0]references. When you loop over c(for i in c:), at some point ialso refers to that same object. the delkeyword removes a single reference, so:

cpython 至少适用于引用计数以确定何时删除对象。在这里，您有对相同对象的多个引用。 a指的是c[0]引用的同一个对象。当您循环c( for i in c:) 时，在某些时候i也指向同一个对象。所述del关键字删除单个参考，所以：

for i in c:
   del i

creates a reference to an object in cand then deletes that reference -- but the object still has other references (one stored in cfor example) so it will persist.

创建对对象的引用c，然后删除该引用——但该对象仍有其他引用（c例如存储在其中的引用），因此它将持续存在。

In the same way:

以同样的方式：

def kill(self):
    del self

only deletes a reference to the object in that method. One way to remove all the references from a list is to use slice assignment:

只删除对该方法中对象的引用。从列表中删除所有引用的一种方法是使用切片赋值：

mylist = list(range(10000))
mylist[:] = []
print(mylist)

Apparently you can also delete the slice to remove objects in place:

显然，您还可以删除切片以删除原位对象：

del mylist[:]  #This will implicitly call the `__delslice__` or `__delitem__` method.

This will remove all the references from mylistand also remove the references from anything that refers to mylist. Compared that to simply deleting the list -- e.g.

这将从中删除所有引用，mylist并从引用 的任何内容中删除引用mylist。与简单地删除列表相比 - 例如

mylist = list(range(10000))
b = mylist
del mylist
#here we didn't get all the references to the objects we created ...
print(b) #[0, 1, 2, 3, 4, ...]

Finally, more recent python revisions have added a clearmethod which does the same thing that del mylist[:]does.

最后，最近的 python 修订版添加了一个clear方法，它可以做同样的事情del mylist[:]。

mylist = [1, 2, 3]
mylist.clear()
print(mylist)

回答by Jon-Eric

Here's how you delete every item from a list.

以下是从列表中删除每个项目的方法。

del c[:]

Here's how you delete the first two items from a list.

以下是从列表中删除前两项的方法。

del c[:2]

Here's how you delete a single item from a list (ain your case), assuming cis a list.

这是从列表中删除单个项目的方法（a在您的情况下），假设c是一个列表。

del c[0]

回答by trojek

To delete all objects in a list, you can directly write list = []

删除一个列表中的所有对象，可以直接写 list = []

Here is example:

这是示例：

>>> a = [1, 2, 3]
>>> a
[1, 2, 3]
>>> a = []
>>> a
[]

回答by trojek

If the goal is to delete the objects aand bthemselves (which appears to be the case), forming the list [a, b]is not helpful. Instead, one should keep a list of strings used as the names of those objects. These allow one to delete the objects in a loop, by accessing the globals()dictionary.

如果目标是删除对象a和b它们本身（似乎是这种情况），则形成列表[a, b]没有帮助。相反，应该保留一个字符串列表，用作这些对象的名称。这些允许通过访问globals()字典来删除循环中的对象。

c = ['a', 'b']
# create and work with a and b    
for i in c:
    del globals()[i]