# Coding a Linked List

Here is code you should copy-paste in a file called `linkedlist.py`:

```python
class Node:
    def __init__(self, data):
        self.data = data
        self.next = None

class LinkedList:
    def __init__(self):
        self.head = None

    def add_to_front(self, data):
        pass

    def pop_from_front(self):
        pass

    def __str__(self):
        pass

    def __getitem__(self, index):
        pass

    def __setitem__(self, index, value):
        pass
```

Notice the functions of the LinkedList class are unimplemented.  Here is what
should happen in each function.

- `add_to_front(self,data)` should add a new Node containing `data` to the
  front of the linked list. Your linked list will be one Node longer after
  calling this function. This function must be $O(1)$.
- `pop_from_front(self)` should remove the first Node of the linked list, and
  return the value of its data. For example, if the linked list contains a
  Node containing 6, and then a Node containing 5, the function should return 6,
  and alter the linked list to now only containing a Node with 5. If the
  linked list is empty, this function should raise an `IndexError`. This
  function must be $O(1)$.
- `__str__(self)` is the function that is called whenever you try to cast a
  linked list object to a string, such as with `str(my_ll)` or `print(my_ll)`.
  This function should return a string with the comma-separated contents of the
  linked list. For example, a linked list with a Node containing 6, and then a
  Node containing 5 would return the string `"6,5"`. This function must be
  $O(n)$.
- `__getitem__(self, index)` is how we overload the square brackets for
  access. For example, `print(my_ll[3])` is equivalent to
  `print(my_ll.__getitem__(3))`. This function should return the contents of
  the `index`th node in the linked list. If `index` is an illegal index (too
  big or too small), the function should raise an `IndexError`. This function
  must be $O(n)$.
- `__setitem__(self, index, value)` is how we overload the square brackets for
  assignment. For example, `my_ll[3]=6` is equivalent to
  `my_ll.__setitem__(3, 6)`. If `index` is an illegal index, the function
  should raise an `IndexError`. This function must be $O(n)$.

Upload your solution to the submit site as project `linkedlist1`. There are
test cases to help you check your work.

[My solution](llCodeHWSoln).