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#Methods & Naming

You're building a collection so, implicitly, you're building a contract with your user that your class will act like a collection, that you'll stick to a protocol for collections objects.

If you wan't to grasp a little more on what I’m trying to say, you can read this article.

So, even though I agree with @Dair that size would be "saffer" as _size (but hey, we’re all responsible adults around here), I strongly disagree with the size property. You should implement it as a __len__ method and use it like:

stuff = LinkedList()
length = len(stuff)

Some other methods can have more common names too:

• add \$->\$ apppend;

• add_at \$->\$ insert or __setitem__:

  __setitem__ will allow you to do stuff[3] = 'some value' and then insert is just a call to self[index] = value.

  You will need to change the signature to def __setitem__(self, key, value).

• remove \$->\$ pop (or maybe __delitem__); remove is prefered to remove by value instead of by index.

• get \$->\$ __getitem__: it will allow you to do the_value = stuff[3]; you should also remove get_node as there is little to no interest in exposing your internals to the user.

#Methods that are missing

You could implement an __iter__ method that will allow you to do:

stuff = LinkedList()
# populate stuff
for elem in stuff: # will use __iter__, or fail back to __len__ + __getitem__ if not available
 do_something(elem)

It will also help you shorten __getitem__. You can use something along the lines of:

def __iter__(self):
 node = self.first
 while node is not None: # No self.size involved, yay
 yield node.value
 node = node.after

You can also implement the __reversed__ iterator using the same logic (and use it in __getitem__ too.

Using a parameter to __init__ that default to None would also be usefull to build a LinkedList out of any iterable:

def __init__(self, other=None):
 self._size = 0
 self.first = None
 self.last = None
 if other is not None:
 for element in other:
 self.append(element)

It is then easy to create stuff = LinkedList([1,2,8,12]).

And finally, you should consider adding a __str__ or __repr__ method so you can print(stuff). Use __iter__ to simplify it.