How to assign a type to a parameter in python?

I have a class named triangulo, and a class named coord. So, in a way to create a new instance of triangle, I pass three vertex like

t= triangle( V1, V2, V3)

So, for documentation, I want to write the class triangle in this way

class triangulo( object ):
   def __init__(self, a:coord, b:coord, c:coord)->None:
       """Constructor
       """
       self.A= a
       self.B= b
       self.C= c

class coord( object ):    
    def __init__( self, x, y ): 
        self.x= x
        self.y= y

But when I try to import this library I get this error

NameError: name ‘coord’ is not defined

So the question is: How can I make python accept vertex as a type of data?

>Solution :

You need to declare the class before using it! so putting coord class on the top of triangulo will solve the problem