[mod_python] Modpython, Apache, Matplotlib which is responsible

Trying to get Apache to display an graph plotfile.png but get an error

The website has 

index.py with links to 

page1.py
page2.py
...
pagen.py

page1.py calls matplotlib to plot some data retrieved from a database.
Matplotlib can't write to the www-data root (permissions problem) so I
have it write to /tmp.
I then copy the file to the www-data root using pexpect.run('cp
plotfile.png'). 
However page1.py fails to display the graph. The error is 
"can't find /page1.py/plotfile.png."  Page1.py is not a directory 
The file has the owner:group of www-data. 

I have verified that the file is in the www-root directory. 

Don't know if it is an issue but page1.py has two frames. One which is
for displaying data. 

Is Apache or Mod_python the cause?

Ron