Python Design Patterns - Adapter

Adapter pattern works as a bridge between two incompatible interfaces. This type of design pattern comes under structural pattern as this pattern combines the capability of two independent interfaces.

This pattern involves a single class, which is responsible to join functionalities of independent or incompatible interfaces. A real life example could be the case of a card reader, which acts as an adapter between memory card and a laptop. You plug in the memory card into the card reader and the card reader into the laptop so that memory card can be read via the laptop.

The adapter design pattern helps to work classes together. It converts the interface of a class into another interface based on requirement. The pattern includes a speciation a polymorphism which names one name and multiple forms. Say for a shape class which can use as per the requirements gathered.

There are two types of adapter pattern −

Object Adapter Pattern

This design pattern relies on object implementation. Hence, it is called the Object Adapter Pattern.

Class Adapter Pattern

This is an alternative way to implement the adapter design pattern. The pattern can be implemented using multiple inheritances.

How to implement the adapter pattern?

Let us now see how to implement the adapter pattern.

class EuropeanSocketInterface:
   def voltage(self): pass

   def live(self): pass
   def neutral(self): pass
   def earth(self): pass

# Adaptee
class Socket(EuropeanSocketInterface):
   def voltage(self):
      return 230

	def live(self):
      return 1
   
   def neutral(self):
      return -1
   
   def earth(self):
      return 0

# Target interface
class USASocketInterface:
   def voltage(self): pass
   def live(self): pass
   def neutral(self): pass

# The Adapter
class Adapter(USASocketInterface):
   __socket = None
   def __init__(self, socket):
      self.__socket = socket
   
   def voltage(self):
      return 110
   
   def live(self):
      return self.__socket.live()
   
   def neutral(self):
      return self.__socket.neutral()

# Client
class ElectricKettle:
   __power = None
   
   def __init__(self, power):
	   self.__power = power
   
   def boil(self):
      if self.__power.voltage() > 110:
         print "Kettle on fire!"
      else:
         if self.__power.live() == 1 and \
            self.__power.neutral() == -1:
            print "Coffee time!"
         else:
            print "No power."

def main():
   # Plug in
   socket = Socket()
   adapter = Adapter(socket)
   kettle = ElectricKettle(adapter)
	
   # Make coffee
   kettle.boil()
	
   return 0
	
if __name__ == "__main__":
   main()

Output

The above program generates the following output −

Explanation

The code includes adapter interface with various parameters and attributes. It includes Adaptee along with Target interface that implements all the attributes and displays the output as visible.