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- [Instructor] In this video,
I'm going to demonstrate

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default parameter values.

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Now, when you're defining
functions in Python,

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it's extremely common to
provide default values

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for each of the parameters you define

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so that people can have the flexibility

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of calling your functions
a number of different ways.

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So for the purpose of this example,

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let's once again jump into ipython,

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and let's define a new function.

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We'll call it rectangle

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area,

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and for a rectangle's area,

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we need to be able to calculate
the length times the width,

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so we need two different
pieces of information

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to perform that calculation.

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So let's define a length parameter,

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and just for argument's
sake, no pun intended,

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let's give the length
a default value of two,

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and let's have a width parameter as well,

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and we'll give that a
default value of three.

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Now, when you're doing default arguments,

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you typically wanna
choose realistic values

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that somebody would normally
want as their default.

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So you might use one for the
length and one for the width,

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or even zero for each of those.

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That would be up to you as
the definer of the function.

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But we want to demonstrate
the basic concept here,

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so we chose some values that we probably

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would not use normally.

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And as we typically do,

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we're going to give this a docstring,

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so return a rectangle's area.

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And the return statement
for this is straightforward.

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We simply want to return
the length times the width.

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So a relatively simple function
definition in this case.

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Now, because of the fact

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that we've provided default arguments,

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we actually have a
couple of different ways

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that we can call this function.

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So we can say let's call rectangle area

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with no arguments whatsoever.

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Now there is no function
defined that takes no arguments,

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but there is a function
defined with the same name

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that has default values for
every one of its parameters.

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So this function call
that I'm about to execute

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is actually going to be treated

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as if I pass in two for the
length and three for the width.

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So let's give that a shot and
we see that we get six back.

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Now, if I call rectangle
area and let's say

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I just pass it a single value, ten,

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in this case, the Python
interpreter is going to take

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that value and use it
as the first parameter

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in the parameter list,

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so the length will be ten,

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and because we're not
supplying a second parameter,

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the width will be three.

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So ten times three should give me 30,

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and indeed it does.

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Now of course we can always
call rectangle area width

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both arguments that we specified,

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in which case it will
simply use those two values

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to calculate the results.

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Now in the next video, we'll
take a look at a concept

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called keyword arguments
and talk about other ways

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in which we could call this same function.