the way of "import"

[smalltalk]

I have three files names t1.py,t2.py,t3.py in e:\test\dir1,of course
dir2 is exsit
the content of t1.py as follow:
t1.py
import os
print 'this is t1.py'
os.chdir('..\\dir2')
the content of t2.py as follow:
print "this is t2.py"
the content of t3.py as follow:
import t1
import t2


if i run t3.py in cmd of windows as follow:
python t3.py

no errors show

if i run t3.py in idle:
>>> import t3
this is t1.py
Traceback (most recent call las
  File "<stdin>", line 1, in <module>
  File "t3.py", line 2, in <module>
ImportError: No module named t2

can you give me a help?