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Being able to identify object classes and types is a really useful ability.
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isinstance(<object>, <class>)- This function will tell you whether or not<object>is an instance of<class>. If it could be an instance of several classes, you can use a tuple of classes like so:isinstance(<object>, (<class1>, <class2>, <class3>)). -
issubclass(<class>, <class>)- This function will tell you whether or not one class is a descendent of another class. Just likeisinstance(), you can use a tuple of classes to compare against. -
type(<instance>)will give you the class for an instance, as willinstance.__class__. Neither of these is particularly useful.
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So far we've been building new classes and
using classes to add attributes and
0:00
methods to our custom classes.
0:04
Let's take a break from creating
classes though and look at a couple of
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useful functions for identifying what
kind of objects we're working with.
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So, these functions aren't necessarily
something you're going to use every day or
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even something you're gonna
wanna use all the time.
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They are, however, really handy when
you need to act a certain way or
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an object,
depending on what kind of object it is.
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If Python is duck typed,
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consider this to be how you separate
the mallards from the mandarins.
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So I'm gonna hop into Python, and
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I'm just gonna show what these do because
they're really fun and interactive.
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The first is probably the one that
you're going to use the most often.
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This function isinstance
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tells you whether or not something is
an instance of a particular class.
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And the string 'a' does
happen to be a string.
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You can use it with multiple types, too.
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So we can say, isinstance,
and let's get the float 5.2,
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and then inside of a new tuple
we can say int or float, and
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we get back True because it
is either an int or float.
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It's a float.
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We can also do isinstance 5.2,
is that a string, a boolean, or a dict?
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No, it's not.
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This also does expose a pretty fun
little fact from Python's past.
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Cuz you can do isinstance True,
and int, and it is.
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I'll leave it up to you to figure
out why or how that came about.
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The second function is issubclass,
issubclass.
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And this one tells you whether or
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not a particular class is
a subclass of another class.
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Like, isinstance,
this can also take a list of classes, or
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rather a couple of classes
to compare against.
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So, (bool, int) True issubclass(str,
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int) False, okay?
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And we can use that to check
the tree of our own classes, too.
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I'm gonna use Ctrl l here,
to clear the screen.
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And I'm gonna say from
thieves import Thief.
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And then I'm gonna say from
characters import Character.
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And then, I'm gonna say issubclass
is Thief is subclass of Character.
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True, since our Thief class
inherits from the Character class,
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our Thief is a subclass of Character,
of course you already knew that.
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The last two items are a bit less useful
but they're still good to know about.
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Firstly, we have the type function.
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Now, type can be used for
some trickier behavior, but
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let's just focus on using it to
get information about an instance.
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So I'm gonna make a new Thief, and
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remember I have to put in
the name argument now.
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And I'm going to say type for kenneth.
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And I get that kenneth is a Thief.
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Now, we already knew that, right?
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But, it's great that Python can tell us.
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The type function tells you the type
of object that an instance is.
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Generally, you'll want to use isinstance,
if you're wanting to know if I whether or
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not to work with an instance though, since
it will check the full inheritance tree.
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If I was to use this,
to find out whether or
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not kenneth was a Character,
I wouldn't know.
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I only know that kenneth is a Thief.
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Now, we've used the __init__
to control how it was created.
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Python's classes have tons
of these magic methods and
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we're gonna talk about several
of them in the next stage.
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Python classes also have a lot
of magic attributes too, and
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one of those is the class attribute.
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It'll tell you what class an instance is.
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So we can say kenneth.__class__ and
get back our thieves.Thief.
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And we can even go a step further and get
the magic name attribute off of the class.
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Kenneth.__class__.__name__, and
that tells us Thief.
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So if you wanted to write some code,
then inspect at an instance's class name,
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you could do it.
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While Python is heavily slanted toward
duck typing, where if an object quacks
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like a duck and waddles like a duck
should be considered a duck.
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I mean, if you can use a method on
an object and not get an exception,
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you should use it that way.
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It's still really handy to be able to
tell if something is an instance of
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a particular class or not.
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You'll find yourself using these functions
and attributes when you get into code
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that operates based on the type
of arguments it's working with.
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Often referred to metaprograming or
introspective programming.
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Both of those are beyond the scope of
this course, but feel free to look
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into them yourself, they're very
interesting ways of programming.
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All right, take a break if you need it,
get a snack if you're hungry,
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do code challenges and
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quizzes to cement all of this knowledge
in your head, then come back for
4:41
the next stage where we'll get our hands
dirty with Python's built in classes.
4:44
Ever wanted dot notation on a dictionary?
4:48
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