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== 11.3#h(0.6em)Instance methods


  
    
=== Learning objectives


    By the end of this section you should be able to


    - Create and implement \_\_init\_\_() with multiple parameters including default parameter values.
- Describe what information an instance method has access to and can modify.


  
  
    
=== More about \_\_init\_\_()


    In Python, \_\_init\_\_() is the special method that creates instances. \_\_init\_\_() must have the calling instance, self, as the first parameter and can have any number of other parameters with or without default parameter values.


    #notebox("Note", rgb("#8a94a6"), rgb("#556666"), rgb("#f7f8fa"))[
#emph[Creating patient vital signs instances]


      #link("https://www.openstax.org/r/creating-instances")[Creating patient vital signs instances; ch 11, video 7]
]


    #notebox("Note", rgb("#8a94a6"), rgb("#556666"), rgb("#f7f8fa"))[
#emph[Defining and using \_\_init\_\_() with parameters]


      Consider the example above.
]


  
  
    
=== Instance methods


    An #strong[instance method] is used to access and modify instance attributes as well as class attributes. All methods shown so far, and most methods defined in a class definition, are instance methods.


    #examplebox("Example 1")[Instance methods are often used to get and set instance information][
class ProductionCar:
    def \_\_init\_\_(self, make, model, year, max\_mph = 0.0):
      self.make = make
      self.model = model
      self.year = year
      self.max\_mph = max\_mph

    def max\_kmh(self):
      return self.max\_mph \* 1.609344

    def update\_max(self, speed):
      self.max\_mph = speed

  car\_1 = ProductionCar('McLaren', 'Speedtail', 2020) \# car\_1.max\_mph is 0.0
  car\_1.update\_max(250.0) \# car\_1.max\_mph is 250.0
  print(car\_1.make, car\_1.model, 'reaches', car\_1.max\_mph, 'mph (',
    car\_1.max\_kmh(), 'km/h)') \# Prints McLaren Speedtail reaches 250.0 mph (402.336 km/h)
]


    #notebox("Note", rgb("#8a94a6"), rgb("#556666"), rgb("#f7f8fa"))[
#emph[CoffeeOrder instance methods]


      Consider the example below:


      
  class CoffeeOrder:
    loc = 'Cafe Coffee'
    cls\_id = 1

    def \_\_init\_\_(self, size=16, milk=False, sugar=False):
      self.order\_id = CoffeeOrder.cls\_id
      self.cup\_size = size
      self.with\_milk = milk
      self.with\_sugar = sugar
      CoffeeOrder.cls\_id += 1

    def change(self, milk, sugar):
      self.with\_milk = milk
      self.with\_sugar = sugar

    def print\_order(self):
      print(CoffeeOrder.loc,'Order', self.order\_id, ':', self.cup\_size, 'oz')
      if self.with\_milk:
        print('\\twith milk')
      if self.with\_sugar:
        print('\\twith sugar')
  
  order\_1 = CoffeeOrder(8)
  order\_2 = CoffeeOrder(8, True, False)
  order\_1.change(False, True)
]


  
  #notebox("Note", rgb("#8a94a6"), rgb("#556666"), rgb("#f7f8fa"))[
#emph[Creating a class for vending machines]


    Write a class, VendingMachine, as described below. Default values follow the attributes. Ex: count's default value is 0. Create a vending machine using a value read from input and call instance methods.


    Instance attributes:


    - count: 0
- max: 0


    Methods:


    - \_\_init\_\_(num): initializes count and max with num parameter
- refill(): assigns count with max's value and prints "Refilled"
- sell(order): assigns count with the value of count minus order and prints "Sold: \[order\]"
- print\_stock(): prints "Current stock: \[count\]"


    Given input:


    
  100
  25
  
    The output is:


    
  Current stock: 100
  Sold: 25
  Current stock: 75
  Refilled
  Current stock: 100
  
    \# Define VendingMachine class 

stock = int(input())
vm = VendingMachine(stock)
vm.print\_stock()
order\_1 = int(input())
vm.sell(order\_1)
vm.print\_stock()
vm.refill()
vm.print\_stock()
]