ReactCHALLENGES

4. Methods

A method is a function defined inside a class. It receives the instance as its first parameter, by convention named self:

  • bark is a method: notice that it is indented inside the class, at the same level as __init__.
  • When you call dog.bark(), Python passes dog as self automatically. You write no argument for self.
  • Inside the method, self.name reads the attribute of that same instance.

Methods can take extra parameters. They come after self, and you pass them normally:

  • The definition has two parameters: self and name.
  • The call has one argument: "Ada". self is automatic.

A method can return a value, exactly like a function, and it can change the instance's attributes:

Coming from JavaScript? Methods are like class methods, but this is not implicit: you write self as the first parameter and use self.attribute. Calling obj.method() is the same.

#01

Call a method

Define a class Greeter with a method hello(self) that prints Hello!. Create greeter = Greeter() and call greeter.hello().

Print exactly:

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#02

Read an attribute inside a method

Define Dog with __init__(self, name) that stores self.name, and a method bark(self) that prints <name> says woof, using self.name. Create dog = Dog("Rex") and call dog.bark().

Print exactly:

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#03

A method with an extra parameter

Define a class Greeter with a method greet(self, name) that prints Hello, <name>!. Create greeter = Greeter() and call greeter.greet("Ada").

The call passes one argument; self is filled in automatically.

Print exactly:

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#04

Return a value from a method

Define Rectangle with __init__(self, width, height) that stores both attributes. Add a method area(self) that returns self.width * self.height. Create rectangle = Rectangle(2, 3) and print rectangle.area().

Print exactly:

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#05

Change the instance from a method

Define Counter with __init__(self) that sets self.value = 0, and a method increment that adds 1 to self.value. Create counter = Counter(), call counter.increment() twice, then print counter.value.

Print exactly:

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