Mutually referencing imports -- impossible?

John Roth johnroth1 at
Sun Jul 13 21:30:23 CEST 2008

On Jul 13, 11:55 am, Matthew Wilson <m... at> wrote:
> I started off with a module that defined a class Vehicle, and then
> subclasses Car and Motorcycle.
> In the Car class,  for some bizarre reason, I instantiated a Motorcycle.
> Please pretend that this can't be avoided for now.
> Meanwhile, my Motorcycle class instantiated a Car as well.
> Then I moved the Car and Motorcycle classes into separate files.  Each
> imported the Vehicle module.
> Then I discovered that my Car module failed because the global
> Motorcycle wasn't defined.  The same problem happened in my Motorcycle
> module.  Car and Motorcycle can't both import each other.
> In the beginning, when all three (Vehicle, Car, and Motorcycle) were
> defined in the same file, everything worked fine.
> I don't know how to split them out in separate files now though and I
> really wish I could because the single file is enormous.
> Any ideas?
> Matt

While it's possible for circular imports to work, it's very dangerous:
it's not always possible to tell what went wrong without tracking down
the process of the import step by step. There are more productive ways
of banging your head against the wall and going insane.

In your situation, it might be a whole lot easier to extract a common
superclass that both of your classes could inherit from.

John Roth

More information about the Python-list mailing list