Free memory in Python

Question

How can I free part of list's memory in python? Can I do it in the following manner:

del list[0:j]  

or for single list node:

del list[j] 

Mark: My script analyzes huge lists and creates huge output that is why I need immediate memory deallocation.

Answer 1

You cannot really free memory manually in Python.

Using del decreases the reference count of an object. Once that reference count reaches zero, the object will be freed when the garbage collector is run.

So the best you can do is to run gc.collect() manually after del-ing a bunch of objects.

---

In these cases the best advice is usually to try and change your algorithms. For example use a generator instead of a list as Thijs suggests in the comments.

The other strategy is to throw hardware at the problem (buy more RAM). But this generally has financial and technical limits. :-)

Answer 2

You can delete an item in list via four popular methods (including collections.deque) :

list remove() method :

remove removes the first matching value, not a specific index

remember This method does not return any value but removes the given object from the list.

example :

list_1 = [987, 'abc', 'total', 'cpython', 'abc'];
list_1.remove('abc')
print(list_1)
list_1.remove('total')
print(list_1)

output:

[987, 'total', 'cpython', 'abc']
[987, 'cpython', 'abc']

Second method is list del() method

You have to specify the index_no here

list_1 = [987, 'abc', 'total', 'cpython', 'abc'];
del list_1[1]
print(list_1)
del list_1[-1:]
print(list_1)

output:

[987, 'total', 'cpython', 'abc']
[987, 'total', 'cpython']

Third one is list pop() method :

pop() removes and returns the last item in the list.

list_1 = [987, 'abc', 'total', 'cpython', 'abc'];
list_1.pop()
print(list_1)
list_1.pop()
print(list_1)
list_1.pop()
print(list_1)

output:

[987, 'abc', 'total', 'cpython']
[987, 'abc', 'total']
[987, 'abc']

Forth method is collections.deque

There are some more external module methods like :

You can pop values from both sides of the deque:

from collections import deque

d = deque()

d.append('1')
d.append('2')
d.append('3')
print(d)

d.popleft()
print(d)
d.append('1')
print(d)

d.pop()
print(d)

output:

deque(['1', '2', '3'])
deque(['2', '3'])
deque(['2', '3', '1'])
deque(['2', '3'])