Mix-in Classes

mixin_example.py

# Avoid using multiple inheritance if mix-in classes can achieve the same outcome.
# Use pluggable behaviors at the instance level to provide per-class customization when mix-in classes may require it.
# Compose mix-ins to create complex functionality from simple behaviors.

class ToDictMixin(object):
    """This class add the ability to serialize an object to a dictionary
    
    Takes each element of self.__dict__ and saves it
    """
    
    def to_dict(self):
        return self._traverse_dict(self.__dict__)
    
    def _traverse_dict(self, instance_dict):
        output = {}
        for key, value in instance_dict.items():
            output[key] = self._traverse(key, value)
        return output
        
    def _traverse(self, key, value):
        # If the object's class has also the Mixin functionality, use the same method
        if isinstance(value, ToDictMixin):
            return value.to_dict()
        # If the object is a dict instance, just copy
        elif isinstance(value, dict):
            return self._traverse_dict(value)
        # If the object is a list instance, apply to each value
        elif isinstance(value, list):
            return [self._traverse(key, i) for i in value]
        # If the object has the __dict__ memeber, parse that dictionary
        elif hasattr(value, ‘__dict__’):
            return self._traverse_dict(value.__dict__)
        else:
            return value
        

class JsonMixin(object):
    """This class serialize into a json and can be combined with previous Mixin"""
    @classmethod
    def from_json(cls, data):
        kwargs = json.loads(data)
        return cls(**kwargs)
    def to_json(self):
        return json.dumps(self.to_dict())
    
    
class DatacenterRack(ToDictMixin, JsonMixin):
    def __init__(self, switch=None, machines=None):
        self.switch = Switch(**switch)
        self.machines = [Machine(**kwargs) for kwargs in machines]
        
class Switch(ToDictMixin, JsonMixin):
    #...
    
class Machine(ToDictMixin, JsonMixin): 
    #...

## Example of serialized switch
serialized = ”””{
       “switch”: {“ports”: 5, “speed”: 1e9},
       “machines”: [
           {“cores”: 8, “ram”: 32e9, “disk”: 5e12},
           {“cores”: 4, “ram”: 16e9, “disk”: 1e12},
           {“cores”: 2, “ram”: 4e9, “disk”: 500e9}
       ] 
}”””

deserialized = DatacenterRack.from_json(serialized)
roundtrip = deserialized.to_json()
   assert json.loads(serialized) == json.loads(roundtrip)