python import error, what's wrong?

[smith jack]

I am using pydev plugin in eclipse, all things works just as well
but now i have confronted with a confusing problem, that is i can
import a module write by myself successfully, but when i try to run
this program,
error just shows up, what's wrong?

the directory structure is as follows:

src
  org.test
      A.py
  org.lab
      B.py


contents of A seems like:
class A
    ...

contents of B seems like:                  // I try to run B.py,
python import error just appears, why?

from org.test.A import A
a = A()