sikuli import function doesn't work

I have two scripts in the same folder.

#content of script2
from sikuli import *
def mypopup():
    popup("hello, I am script2")

#content of script1
import script2
script2.mypopup()

but after run script1, I got a error:
[error] script [ script1 ] stopped with error in line 2
[error] NameError ( global name 'popup' is not defined )
[error] --- Traceback --- error source first line: module ( function ) statement 3: script2 ( mypopup ) def mypopup():
[error] --- Traceback --- end --------------

Is there any problem in the script?How can I solve this issue?