Get a pointer to a list element

Question

I was wondering if it was possible to get a \"pointer\" to an element in a python list. That way, I would be able to access my element directly without needing to know my el

Answer 1

element = mylist[0] already works if you don't need to change the element or if element is a mutable object.

Immutable objects such as int objects in Python you can not change. Moreover, you can refer to the same object using multiple names in Python e.g., sys.getrefcount(1) is ~2000 in a fresh REPL on my system. Naturally, you don't want 1 to mean 2 all of a sudden in all these places.

If you want to change an object later then it should be mutable e.g., if mylist[0] == [1] then to change the value, you could set element[0] = 2. A custom object instead of the [1] list could be more appropriate for a specific application.

As an alternative, you could use a dictionary (or other namespace objects such as types.SimpleNamespace) instead of the mylist list. Then to change the item, reference it by its name: mydict["a"] = 2.

Answer 2

There's no concept of pointers on python (at least that I'm aware of).

In case you are saving objects inside your list, you can simply keep a reference to that object.

In the case you are saving primitive values into your list, the approach I would take is to make a wrapper object around the value/values and keep a reference of that object to use it later without having to access the list. This way your wrapper is working as a mutable object and can be modified no matter from where you are accesing it.

An example:

class FooWrapper(object):
    def __init__(self, value):
         self.value = value

# save an object into a list
l = []
obj = FooWrapper(5)
l.append(obj)

# add another object, so the initial object is shifted
l.insert(0, FooWrapper(1))

# change the value of the initial object
obj.value = 3
print l[1].value # prints 3 since it's still the same reference