python/exercises/simple-linked-list/README.md

# Simple Linked List

Write a simple linked list implementation that uses Elements and a List.

The linked list is a fundamental data structure in computer science,
often used in the implementation of other data structures. They're
pervasive in functional programming languages, such as Clojure, Erlang,
or Haskell, but far less common in imperative languages such as Ruby or
Python.

The simplest kind of linked list is a singly linked list. Each element in the
list contains data and a "next" field pointing to the next element in the list
of elements.

This variant of linked lists is often used to represent sequences or
push-down stacks (also called a LIFO stack; Last In, First Out).

As a first take, lets create a singly linked list to contain the range (1..10),
and provide functions to reverse a linked list and convert to and from arrays.

When implementing this in a language with built-in linked lists,
implement your own abstract data type.

## Hints

To support `list()`, see [implementing an iterator for a class.](https://docs.python.org/3/tutorial/classes.html#iterators)

Additionally, note that Python2's `next()` has been replaced by `__next__()` in Python3. For dual compatibility, `next()` can be implemented as:

```Python
def next(self):
    return self.__next__()
```


## Exception messages

Sometimes it is necessary to raise an exception. When you do this, you should include a meaningful error message to
indicate what the source of the error is. This makes your code more readable and helps significantly with debugging. Not
every exercise will require you to raise an exception, but for those that do, the tests will only pass if you include
a message.

To raise a message with an exception, just write it as an argument to the exception type. For example, instead of
`raise Exception`, you should write:

```python
raise Exception("Meaningful message indicating the source of the error")
```

## Running the tests

To run the tests, run the appropriate command below ([why they are different](https://github.com/pytest-dev/pytest/issues/1629#issue-161422224)):

- Python 2.7: `py.test simple_linked_list_test.py`
- Python 3.4+: `pytest simple_linked_list_test.py`

Alternatively, you can tell Python to run the pytest module (allowing the same command to be used regardless of Python version):
`python -m pytest simple_linked_list_test.py`

### Common `pytest` options

- `-v` : enable verbose output
- `-x` : stop running tests on first failure
- `--ff` : run failures from previous test before running other test cases

For other options, see `python -m pytest -h`

## Submitting Exercises

Note that, when trying to submit an exercise, make sure the solution is in the `$EXERCISM_WORKSPACE/python/simple-linked-list` directory.

You can find your Exercism workspace by running `exercism debug` and looking for the line that starts with `Workspace`.

For more detailed information about running tests, code style and linting,
please see the [help page](http://exercism.io/languages/python).

## Source

Inspired by 'Data Structures and Algorithms with Object-Oriented Design Patterns in Ruby', singly linked-lists. [http://www.brpreiss.com/books/opus8/html/page96.html#SECTION004300000000000000000](http://www.brpreiss.com/books/opus8/html/page96.html#SECTION004300000000000000000)

## Submitting Incomplete Solutions

It's possible to submit an incomplete solution so you can see how others have completed the exercise.