How to dump user defined python objects to json file? By Objects I mean actual objects and not their attributes

So I have two user defined python classes shown below

class cell(object):
def __init__(self,id,x_cor,y_cor,width = cell_size,height = cell_size ,color = lightblue ):
    self.id = id
    self.x_cor = x_cor
    self.y_cor = y_cor
    self.width = width
    self.height = height
    self.color = color

class edge(object):
def __init__(self,pos, x_cor,y_cor,state,color = lightgreen):
    global border_size
    global cell_size
    self.pos = pos
    self.x_cor = x_cor
    self.y_cor = y_cor
    self.state = state
    self.color = color
    if self.state == "H":
        self.width = cell_size+(border_size)*2
        self.height = border_size
        self.x_lower_bound = self.x_cor + border_size
        self.x_upper_bound = self.x_cor +border_size+ cell_size
        self.y_lower_bound = self.y_cor
        self.y_upper_bound = self.y_cor + border_size
    elif self.state == "V":
        self.width = border_size
        self.height = cell_size+(border_size*2)
        self.x_lower_bound = self.x_cor
        self.x_upper_bound = self.x_cor + border_size
        self.y_lower_bound = self.y_cor + border_size
        self.y_upper_bound = self.y_cor + border_size + cell_size

Now I have a 2-D list called cells It is defined and looks like this Click me.

It is a bit messy but you can see that it is a 16 by 16 matrix storing an object od cell as defined above

No i want to store this 2-D array in json file this is what i am doing

json_data = []
json_data.append(cells)
with open("default.json" , "w") as f:
    json.dump(json_data,f,indent = 2)

This is the error on terminal I am getting Click on the link to view