Debian – cannot reinstall python2.6

I am trying to reinstall python2.6 on debian 6 but I get:

root@ff: apt-get install --reinstall python2.6
Reading package lists... Done
Building dependency tree       
Reading state information... Done
You might want to run 'apt-get -f install' to correct these:
The following packages have unmet dependencies:
 python-pkg-resources : Depends: python (< 2.7) but 2.7.5-5 is to be installed
 python-setuptools : Depends: python (< 2.7) but 2.7.5-5 is to be installed
E: Unmet dependencies. Try 'apt-get -f install' with no packages (or specify a solution).

Notice that starting python2.6 works fine:

:~$ python2.6
Python 2.6.6 (r266:84292, Dec 26 2010, 22:31:48) 
[GCC 4.4.5] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> 

But its the application that I need to use which depend on python that is now broken, e.g pip:

~$ pip
Traceback (most recent call last):
  File "/usr/bin/pip", line 7, in <module>
    from pip.log import logger
ImportError: No module named pip.log

I previously installed python2.7 and have used:

update-alternatives –config python

to switch back to 2.6.But it seems that application installed using python 2.6 has been corrupted by the 2.7 install.

I have tried to uninstall python2.7. But it says that its not installed, even though I can start it from a terminal:

# apt-get purge python2.7
Reading package lists... Done
Building dependency tree       
Reading state information... Done
Package python2.7 is not installed, so not removed
0 upgraded, 0 newly installed, 0 to remove and 460 not upgraded.
# python
Python 2.7.6 (default, Jan 11 2014, 14:34:26) 
[GCC 4.8.2] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> 

It seems that a complete re-install of the system is required, but I would like to avoid that if possible.

And also tried restoring an older status file :

# cp /var/backups/dpkg.status.2  /var/lib/dpkg/status
# apt-get clean
# apt-get update

And my /etc/apt/sources list:

# deb cdrom:[Debian GNU/Linux 6.0.4 _Squeeze_ - Official amd64 NETINST Binary-1 20120129-00:39]/ squeeze main

#deb cdrom:[Debian GNU/Linux 6.0.4 _Squeeze_ - Official amd64 NETINST Binary-1 20120129-00:39]/ squeeze main

deb http://ftp.se.debian.org/debian/ squeeze main
deb-src http://ftp.se.debian.org/debian/ squeeze main

deb http://security.debian.org/ squeeze/updates main
deb-src http://security.debian.org/ squeeze/updates main

# squeeze-updates, previously known as 'volatile'
deb http://ftp.se.debian.org/debian/ squeeze-updates main
deb-src http://ftp.se.debian.org/debian/ squeeze-updates main
deb http://mirror.cse.iitk.ac.in/debian/ testing main contrib

Now of I try to install python-twisted I get:

# apt-get install python-twisted
Reading package lists... Done
Building dependency tree       
Reading state information... Done
The following packages were automatically installed and are no longer required:
  iso-codes libserf-0-0 python-apt-common lsb-release
Use 'apt-get autoremove' to remove them.
The following extra packages will be installed:
  cpp-4.4 g++-4.4 gcc-4.4 gcc-4.4-base gcc-4.8-base libapr1 libapr1-dev libaprutil1 libaprutil1-dbd-sqlite3 libaprutil1-dev libaprutil1-ldap libc-dev-bin libc6
  libc6-dbg libc6-dev libc6-i386 libdb5.1 libexpat1 libexpat1-dev libffi6 libgcc1 libgmp10 libgomp1 liblzma5 libmpfr4 libpython-dev libpython-stdlib
  libpython2.7 libpython2.7-dev libpython2.7-minimal libpython2.7-stdlib libsasl2-2 libsasl2-modules libsasl2-modules-db libsctp-dev libsctp1 libserf-1-1
  libsqlite3-0 libsqlite3-dev libssl1.0.0 libstdc++6 libstdc++6-4.4-dev libsvn1 libtinfo5 libxml2 linux-headers-2.6.32-5-common locales make multiarch-support
  python python-crypto python-dev python-libxml2 python-lxml python-minimal python-openssl python-pkg-resources python-setuptools python-sqlite python-support
  python-svn python-twisted-bin python-twisted-conch python-twisted-core python-twisted-lore python-twisted-mail python-twisted-names python-twisted-news
  python-twisted-runner python-twisted-web python-twisted-words python-yaml python-zope.interface python2.7 python2.7-dev python2.7-minimal subversion

The above list contains a bunch of python2.7 dependencies….where do they come from? Should it not be possible to install python-twisted for python2.6?