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Methods
10:37Learn how to add functions to a class in Python.
In object-oriented Python, a function
inside of a class is called a method.
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In this video, we're going to dive
into how to add methods to a class,
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pass in arguments and call a method.
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Let's start by adding
a method to this car class.
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It will be called stop
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The format is the same as
a regular function, but
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it needs to take self as an argument.
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All methods inside of a class will need to
take self, otherwise it'll throw an error.
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Inside of our method,
let's just print out "The car has stopped".
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Let's jump down here and call our method.
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In order to call it,
we will need our instance and
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dot notation plus
the name of the function.
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So, car_one.stop().
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Run the file.
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And voila, it printed out our message.
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Now, what if we needed to pass
in information to our method?
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How do we do that?
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Well, it works just like
a regular function.
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Let's create a new method called go.
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It'll take self and a speed argument.
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And then print out an f string,
"The car is going" and pass in the speed.
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Cool, now let's call this method a few
times and pass in a few different speeds.
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Go ahead and try it on your own,
pass in whatever speeds you like.
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Okay, so we've tackled creating a method,
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calling a method and
passing an argument so far.
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It's time for
you to give it a go on your own.
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Create a class, add a method that
takes at least one argument.
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Give it some logic or
a simple print statement and then call it.
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If you get stuck, rewind me and
rewatch this video.
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It's okay if it takes you a few times for
things to click.
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I'll see you back here in a bit.
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Back?
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Let's keep going.
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A powerful thing about classes is
we can use our attributes inside of
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any method we have.
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Let's add a new instance attribute
called is moving and set it to false.
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Instance attributes don't
always have to be passed in.
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Now we can adjust our stop and
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go methods to check this attribute
first before printing a message.
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That way we don't tell
a stopped car to stop more cuz
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that wouldn't really make any sense.
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In our stop method,
let's check if the car is moving.
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If it is,
let's print out that the car has stopped
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And then set our is
moving attribute to false
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Otherwise, let's let them know
the car has already stopped.
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Inside of our go method,
let's do something similar.
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If is moving is false, which means
we need to check for, not is moving.
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Then let's let the user know
the car has started moving and
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set the attribute to true.
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We can print out the car's speed
outside of the statement, so
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the speed can be changed
if the user wants.
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Nice.
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Let's call both methods a few
times to see our work in action.
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Run the file.
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Take a minute to follow the logic
of what's happening in the console
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with the code you just wrote.
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For example, when is instance is created,
is moving is set to false.
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So when stop is called, we get the
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"The car is all ready stopped" message.
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When go is called,
is_moving is set to True and
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we get "The car starts moving" and
our speed message.
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Keep following the rest
of the logic on your own.
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This helps you make sure you know
what is happening with your code.
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Go ahead and pause me.
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Nice work.
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One last challenge to tackle.
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If the car is moving,
then it's using up gas.
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Let's create a new instance
attribute called gas.
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Now let's create a method called use_gas.
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Inside of the method, reduce the gas
value by 50, to make it easier to test.
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Then return False if the self.gas
value is less than or equal to zero.
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And True, if there's still gas.
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Now we can use this method
inside our go method.
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If the car is moving,
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then we need to call our use_gas method
to reduce the amount of gas we have.
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If we are out of gas then
the car cannot move at all.
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At the start of this method,
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let's check if we have gas by calling
the method using self in an if statement.
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This both calls the method and
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lets us know if we still
have gas at the same time.
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If we have gas,
then we can run the logic we already had.
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Otherwise, we need to let the user
know they've run out of gas and
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call the stop function to stop the car.
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Go ahead and run the file to see
what's changed in the console.
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Take a minute again to think through
what's happening in the console and
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follow the logic in your code.
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When you feel comfortable that
you understand what's happening,
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then unpause me.
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It's recap o'clock.
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In this video,
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you've learned how to add functions to
your class, which are called methods.
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They follow the same syntax
as regular functions, but
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are placed inside of a class and
take self as an argument.
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You can pass in values to a method,
call other methods
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inside of one and
access attributes of your class.
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When calling a method, you use dot
notation on an instance of the class.
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Don't forget to pass in values
if the method calls for them.
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Try out what you've learned so
far on your own.
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Create your own class, add attributes,
methods and play around.
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This is how you learn and
solidify your new knowledge.
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Also, try helping someone else.
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Nothing helps us realize
how much we know or
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don't know, by helping someone else learn.
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Lastly, never feel bad if
you need to rewatch a video.
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Some concepts may be harder than others
and there's no judgment on how many
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times you needed to watch a video
before the concept finally clicked.
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Take as long as you need and
reach out if you hit a roadblock.
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We're here to help.
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