Can not import stackless after stackless python installation

Question

I used pycharm and eclipse+pydev, and I also installed stackless python(2.7.1) for mac os x. when I try to import stackless, there always are tips which is "can't find such package/reference", but when I switch to IDLE/Client, "import stackless" is correct. I really don't know the reason, please help me. thanks a lot