How to remove one old python installation from a system with multiple (non-system) installations of python
From python docs noting that they seem to have hard coded 2.5 instead of the current version and is not that well written


  What you get after installing is a number of things:
  
  A MacPython 2.5 folder in your Applications folder. In here you find
  IDLE, the development environment that is a standard part of official
  Python distributions; PythonLauncher, which handles double-clicking
  Python scripts from the Finder; and the “Build Applet” tool, which
  allows you to package Python scripts as standalone applications on
  your system.
  
  A framework /Library/Frameworks/Python.framework, which
  includes the Python executable and libraries. The installer adds this
  location to your shell path. To uninstall MacPython, you can simply
  remove these three things. A symlink to the Python executable is
  placed in /usr/local/bin/.


so remove 

/Applications/Python 3.1
/Library/Frameworks/Python.framework/Versions/3.1
/usr/local/bin/python31 (I use a different install so this might be python3.1 or similar)