factory method broken into modules

I have been looking at the simple factory example,

from __future__ import generators
import random

class Shape(object):
    # Create based on class name:
    def factory(type):
        #return eval(type + "()")
        if type == "Circle": return Circle()
        if type == "Square": return Square()
        assert 0, "Bad shape creation: " + type
    factory = staticmethod(factory)

class Circle(Shape):
    def draw(self): print("Circle.draw")
    def erase(self): print("Circle.erase")

class Square(Shape):
    def draw(self): print("Square.draw")
    def erase(self): print("Square.erase")

# Generate shape name strings:
def shapeNameGen(n):
    types = Shape.__subclasses__()
    for i in range(n):
        yield random.choice(types).__name__

shapes = \
  [ Shape.factory(i) for i in shapeNameGen(7)]

for shape in shapes:
    shape.draw()
    shape.erase()

And have tried to break it into separate files.

main.py

from __future__ import generators
import random

from factory.shapes.circle import Circle
from factory.shapes.sqaure import Square


class Shape(object):
    # Create based on class name:
    def factory(type):
        #return eval(type + "()")
        if type == "Circle": return Circle()
        if type == "Square": return Square()
        assert 0, "Bad shape creation: " + type
    factory = staticmethod(factory)


# Generate shape name strings:
def shapeNameGen(n):
    types = Shape.__subclasses__()
    for i in range(n):
        yield random.choice(types).__name__

shapes = \
  [ Shape.factory(i) for i in shapeNameGen(7)]

for shape in shapes:
    shape.draw()
    shape.erase()

circle.py

from __future__ import generators
import random

from factory.main import Shape

class Circle(Shape):
    def draw(self): print("Circle.draw")
    def erase(self): print("Circle.erase")

square.py

from __future__ import generators
import random

from factory.main import Shape

class Square(Shape):
    def draw(self): print("Square.draw")
    def erase(self): print("Square.erase")

and when running it I get ImportError: cannot import name 'Circle'

So although the example works when all the classes are in same module, it seem to have issues when imported them from separated modules. Any ideas?