Make sure you're running it as root as well, it could be a permissions issue; but yes i would sudo mkdir -p /etc/apt/preferences.d/;sudo apt-get clean && sudo apt-get update && sudo apt-get -f install .
Definitely looks like the package exists--
$ links -dump 'http://archive.debian.org/debian-security/pool/updates/main/p/python2.7/' | grep -i 'python2.7-dev_2.7.3-6+deb7u4_armel.deb '
[ ] python2.7-dev_2.7.3-6+deb7u4_armel.deb 2017-11-24 27M
Pretty sure an update will fix it.