This script cleans a directory containing debian packages up leaving only the three newest versions. Package filenames must follow "<package>_<version>-<build>.deb" format and package name must not contain underscores.

gistfile1.py

#!/usr/bin/env python

import sys, os

def extract_pkg(package_file):
  result = {}
  package_file = package_file.replace('.deb', '')
  (result['package'], tmp) = package_file.split('_')
  (tmp, result['build']) = tmp.split('-')
  tmp = tmp.split('.')
  result['version'] = 0.0
  for i in range(0, len(tmp)):
    result['version'] = result['version'] + float(tmp[i]) / 1000**i
  return result

def main(argv=sys.argv):
  packages = os.listdir(argv[1])
  
  basenames = []
  [ basenames.append(name.split('_')[0]) for name in packages if '.deb' in name and not basenames.count(name.split('_')[0]) ]
  
  for package in basenames:
    package_files = [ name for name in packages if package in name ]
    package_files.sort(lambda x, y: cmp(extract_pkg(y)['version'], extract_pkg(x)['version']))
    old_files = package_files[3:]
    for filename in old_files:
      os.unlink(os.path.realpath(os.path.join(argv[1], filename)))
  
if __name__ == "__main__":
  sys.exit(main())