In [11]:
class Computer:

    def __init__(self,model,mem):
        self.model = model
        self.initial_memory = mem
        self.additional_memory = []

    def __str__(self):
        total_memory = self.initial_memory + sum(self.additional_memory)
        return self.model + ":" + str(self.initial_memory)+":"+str(total_memory)

    def add_memory(self,mem):
        self.additional_memory.append(mem)
In [12]:
c1 = Computer("Dell",8)
c2 = Computer("Mac",16)
In [13]:
print(c1)

Dell:8:8
In [14]:
c1.add_memory(16)
In [15]:
print(c1)

Dell:8:24
In [ ]:
c1.additional_memory += 100
print(c1)
c1.add_memory(-100)
print(c1)

Dell:108:124
Dell:108:24