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[MUSIC]

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Now that we have a handle on creating
classes, let's talk about one of the most

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powerful features of Python's classes,
magic methods.

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You've already seen one magic method,
the __init__ one,

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remember we call it magic because it's
a method that Python will call for you.

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As you can probably imagine, there
are tons of Magic Methods that Python uses

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behind the scenes to
make things run smoothly.

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You'll be learning about some of them, but

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I've linked to the full documentation
about them in the teacher's notes.

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I really like Magic Methods,
because despite their name,

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they let us peel back some of the magic
in Python and see how things are working.

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One of the things that happens behind
the scenes, is conversion between types.

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Think about when you use
the str function on an integer.

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What happens?

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It's actually controlled
by a Magic Method.

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Let's go to WorkSpaces and check it out.

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Let's start with our
illustrious Thief class.

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Right now if we turn
a Thief into a string,

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we get something that's well,
less than useful.

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Not really that great.

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So remember that the 0x blah, blah,

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blah bit refers to where
the object is stored in memory.

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Handy but not really handy.

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Wouldn't it be easier to have it
tell us the name of the character?

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Well, let's make it do that then.

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I think this is probably something we'd
want all characters to have though,

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so we'll do it on the Character class and
not on the Thief class.

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You'll often find the implement
Magic Methods on your base classes, but

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not on your specific
implementation classes.

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Those that you use directly,

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usually only have very specific code
that they need to do their jobs.

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The more generic code goes into
the parent classes further up the chain.

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So let's add a new method here.

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And we'll call it __str__.

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As you probably could have guessed.

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So we actually don't need that line.

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So this method should return
a string that you want to use to

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identify your object,
whenever it's turned into a string.

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So in this case, let's return.

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Let's return two things.

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Let's return the self.__class__.__name__,
so we can see if it's a thief,

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or an archer, or a barbarian, or
whatever and let's return self.name.

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So now, if we recheck what
happens when we run play.py.

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We see Thief: Kenneth, so that's awesome,
that's very cool, that's much,

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much friendlier, and it's better output.

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A related method that's often on
a written is __repr__, __repr__

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which is used to give the official
string representation of an instance.

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Now this was mostly used for debugging and

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should present as much useful
information as possible.

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Right now, our rpg gives back what
our old string looked like, and

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I think that's good output for it,
so I'm gonna leave that alone.

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So that's converting to a string,
but what about other conversions?

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More complex conversions, like turning
an instance into a dictionary or

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other object while possible,
are beyond the scope of this course.

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We can though easily set up
converting our objects into floats.

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Now I don't think any of our existing
classes would work well for this, so

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let's make a new one.

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And we'll do this out here in the OO
Python directory not in the rpg directory.

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Now I'm going to call this numstring.py.

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Let's make a class that holds a number,
holds an int or a float, or

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whatever as a string.

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But, it'll let us turn it into
an int whenever we want to.

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Let's just do this, so we'll say class
NumString, cuz that's a catchy name.

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And then def __init__ (self and value).

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And self.value = str (value).

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And then we'll define the __str__,
and we'll return self.value.

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And we'll define __int__, and
we'll return the int(self.value).

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And let's also define __float__,
which returns the float(self.value).

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Now, I'm sure you could guess
what __int__ and __float__ did.

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Even before I told you.

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Since you've seen __str__.

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But it's still good to see them.

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Hopefully, you can see why you probably
wouldn't want to use this as real code.

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It's good for experimentation though.

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You should always play around, and

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try just whatever silly
ideas you can come up with.

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So, in the interest of being silly,
let’s try it out.

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Let’s come down here,
and then go into python.

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And I’m going to say from
numstring import NumString.

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And I’m going to say five = NumString (5).

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And if I look at five,
I get back to this NumString object.

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So if I do a str(five) and
there's '5' as a string.

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And if I print(five),

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I get the string version printed
out which drops the quote marks.

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What if we do int(five), then we get
back a 5, and what if we do float(five)?

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Then we get back 5.0.

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So cool.

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We have an object that represents
itself as a string, but

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that we can turn into a float or init.

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Now, how is this different from
any other number in a string?

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It's not.

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But hopefully you've gotten
a peek behind the curtain here.

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Now what happens if we try and
do some math with our NumString.

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Any guesses before I type this out?

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So I'm going to clear
the screen real quick.

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So let's try five + 4.

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Type error.

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We can't add NumStrings at int.

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Fair enough, so what if we do five
+ a NumString that represents four?

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Can't add NumStrings, another type error.

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What about five + the string of '4'?

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Type error.

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Seems like no matter what I do,
I can't do any math with it.

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Let's see if we can fix
that in the next video.