[Tutor] Making Doubly Linked List with Less Lines of Code.

Danny Yoo dyoo at hashcollision.org
Thu Dec 25 06:15:25 CET 2014

Quick comment: the structure of the code here catches my eye:

>         # Each variable below is a link to the head Node in the respective
>         # row or column.
>         self.row0 = None
>         self.row1 = None
>         self.row2 = None
>         self.row3 = None
>         self.row4 = None
>         self.row5 = None
>         self.row6 = None
>         self.row7 = None
>         self.row8 = None
>         self.row9 = None

It seems highly regular; the code here is maintaining a collection of
row variables.  Because it's so regular, you might consider using a
list to represent this collection.  Concretely:

    self.rows = [None, None, None, None, None, None, None, None, None, None]

We can express this more concisely in Python as:

    self.row = [None] * 10

Once we have this, then we can get at any particular row through its
offset.  So instead of:


we say:


The big win with a list representation is that the offset can be
computed.  So if we need to do an operation on each row, we might say:

    for i in range(10):
        ## ... Do something with self.row[i]

And if you see the full power of this, you'll realize that this allows
us to express loops to do something to _all_ the rows, expressing that
action just once.  Or if we need to do something for every other row,
that too is not too difficult to express:

    for i in range(0, 10, 2):
        ## ... Do something with self.row[i]

In contrast, doing the same thing without using an explicit container
representation means that doing container-wide actions is harder to
do.  This is the code smell that we saw at the beginning of this post,
where we see repetitive code.

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