Inheritance

class Puppy < Dog — one parent, always

Ruby inheritance reads almost exactly like Python's: class Child < Parent. The < means "inherits from" — every method and ivar-setting behavior on Dog is available on Puppy for free:

class Dog
  attr_accessor :name

  def initialize(name)
    @name = name
  end

  def speak
    "#{@name} makes a sound"
  end
end

class Puppy < Dog
end

mochi = Puppy.new("Mochi")
puts mochi.speak       # Mochi makes a sound — inherited, unchanged
puts mochi.is_a?(Dog)  # true — a Puppy IS a Dog

Be honest about the limit: Ruby is single-inheritance — class Puppy < Dog means exactly one parent, full stop. There's no class Puppy < Dog, Trainable like some languages allow. (Modules, next lesson, are Ruby's answer to needing more than one source of shared behavior.)