scipy code runs in empty directory, not another

[Beliavsky]

After installing numpy, scipy, and matplotlib for python 2.6 and
running the code from http://www.scipy.org/Cookbook/OptimizationDemo1
(stored as xoptimize.py) in a directory with other python codes, I got
the error messages

C:\python\code\mycode>python xoptimize.py
Traceback (most recent call last):
  File "xoptimize.py", line 3, in <module>
    from pylab import *
  File "c:\python26\lib\site-packages\pylab.py", line 1, in <module>
    from matplotlib.pylab import *
  File "c:\python26\lib\site-packages\matplotlib\__init__.py", line
133, in <module>
    import sys, os, tempfile
  File "c:\python26\lib\tempfile.py", line 34, in <module>
    from random import Random as _Random
  File "C:\python\code\mycode\random.py", line 1, in <module>
    from RandomArray import standard_normal
  File "C:\python\code\mycode\RandomArray.py", line 1, in <module>
    import ranlib
ImportError: No module named ranlib

When I create a new directory, copy xoptimize.py there, and run, the
program works. Can someone explain why other files are "interfering"
in the first case? Thanks.