how to release used memory immediately in python list?

Question

in many cases ,you are sure you definitely won\'t use the list again,i hope the memory should be release right now

a = [11,22,34,567,9999]
del a

Answer 1

Python uses Reference Count to manage its resource.

import sys
class foo:
    pass

b = foo()
a = [b, 1]

sys.getrefcount(b)  # gives 3
sys.getrefcount(a)  # gives 2

a = None  # delete the list
sys.getrefcount(b)  # gives 2

In the above example, b's reference count will be incremented when you put it into a list, and as you can see, when you delete the list, the reference count of b get decremented too. So in your code

def release_list(a):
   del a[:]
   del a

was redundant.

In summary, all you need to do is assigning the list into a None object or use del keyword to remove the list from the attributes dictionary. (a.k.a, to unbind the name from the actual object). For example,

a = None # or
del a

When the reference count of an object goes to zero, python will free the memory for you. To make sure the object gets deleted, you have to make sure no other places reference the object by name, or by container.

sys.getrefcount(b) # gives 2

If sys.getrefcount gives you 2, that means you are the only one who had the reference of the object and when you do

b = None

it will get freed from the memory.