[Tutor] How does import work?

[Johan Nilsson]

Hi all,

I am rather new to python. I am trying to write a program using the 
scipy package. I have come across a problem that confuses me, and I hope 
that someone could give me an hint on how to solve this.

Here is what I do

Start idle

 >>> from scipy.signal.signaltools import *

/Traceback (most recent call last):
  File "<pyshell#0>", line 1, in -toplevel-
    from scipy.signal.signaltools import *
ImportError: No module named signaltools/

So I try the methodic way and this works, giving me access to the 
functions I need

 >>> from scipy import *
 >>> from scipy.signal import *
 >>> from scipy.signal.signaltools import *

Now what confuses me is that when I put the above three lines in a file 
(of course without the >>>) and execute them I get a long error message.

/ Traceback (most recent call last):
  File "/home/johan/pyton/import_test.py", line 5, in -toplevel-
    from scipy.signal import *
  File "/usr/local/lib/python2.3/site-packages/scipy_base/ppimport.py", 
line 270, in __getattr__
    module = self._ppimport_importer()
  File "/usr/local/lib/python2.3/site-packages/scipy_base/ppimport.py", 
line 233, in _ppimport_importer
    raise PPImportError,\
PPImportError: Traceback (most recent call last):
  File "/usr/local/lib/python2.3/site-packages/scipy_base/ppimport.py", 
line 243, in _ppimport_importer
    module = __import__(name,None,None,['*'])
  File "/usr/lib/python2.3/site-packages/scipy/signal/__init__.py", line 
11, in ?
  File "/usr/lib/python2.3/site-packages/scipy/signal/ltisys.py", line 
14, in ?
  File "/usr/local/lib/python2.3/site-packages/scipy_base/ppimport.py", 
line 270, in __getattr__
    module = self._ppimport_importer()
  File "/usr/local/lib/python2.3/site-packages/scipy_base/ppimport.py", 
line 233, in _ppimport_importer
    raise PPImportError,\
PPImportError: Traceback (most recent call last):
  File "/usr/local/lib/python2.3/site-packages/scipy_base/ppimport.py", 
line 243, in _ppimport_importer
    module = __import__(name,None,None,['*'])
  File "/usr/lib/python2.3/site-packages/Numeric/Matrix.py", line 5, in ?
    import LinearAlgebra
  File 
"/usr/local/lib/python2.3/site-packages/Numeric/LinearAlgebra.py", line 
8, in ?
    import lapack_lite
ImportError: 
/usr/local/lib/python2.3/site-packages/Numeric/lapack_lite.so: undefined 
symbol: dgesdd_/

What I dont understand is how can the import statements work, when I 
type them in manually in IDLE and not when I execute them in a file? Has 
anyone come across this type of behavior before?

Johan