The update from Ubuntu 13.04 to 13.10 failed for me with the error message:
Your python install is corrupted. Please fix the /usr/bin/python symlink.
The reason was that I used update-alternatives to manage my two Python versions (2.7 and 3.3). The following solved the issue for me:
sudo update-alternatives --remove-all python
sudo ln -sf /usr/bin/python2.7 /usr/bin/python
(The expected version can be found out via: python /usr/share/python/pyversions.py -i)
-  One of many forum entries that describes this solution