How to inherit class from different file?

Ok it's not exactly clear what's going wrong because you haven't sent us precisely what you are doing, but here is my guess. If your circle.py file is as follows

import fig
class Circle(Fig):
    def __init__(self, radius):
        self.name= "Circle"
        self.data= ["Radius: ", radius]

This will break because python doesn't know where to find Fig. If instead you write

import fig
class Circle(fig.Fig):
    def __init__(self, radius):
        self.name= "Circle"
        self.data= ["Radius: ", radius]

or

from fig import Fig
class Circle(Fig):
    def __init__(self, radius):
        self.name= "Circle"
        self.data= ["Radius: ", radius]

Everything should work fine. This is because you either have to tell python the namespace through which it can access the class (my first solution) or explicitly import the class (my second solution). The same logic applies if you want to use PI:

import fig
class Circle(fig.Fig):
    def __init__(self, radius):
        self.name= "Circle"
        self.data= ["Radius: ", radius]
        #use PI from fig.py by informing python of namespace
        self.circumference = 2.*fig.PI*radius 

or

from fig import Fig, PI
class Circle(fig):
    def __init__(self, radius):
        self.name= "Circle"
        self.data= ["Radius: ", radius]
        #PI is now explicitly imported so don't need namespace
        self.circumference = 2.*PI*radius

You need to do from fig import FIG in your circle.py. Also make sure that you have __init__.py file present in the folder which is having circle.py and fig.py.

Please also take as look at:

• Importing a function from a class in another file?
• What is __init__.py for?