$ emerge -pvtuD world

These are the packages that would be merged, in reverse order:

Calculating world dependencies... done!
[ebuild     U ] net-im/pidgin-2.2.2 [2.2.1] USE="dbus gtk ncurses nls perl -bonjour -debug -doc -eds -gadu -gnutls -groupwise -gstreamer -meanwhile (-networkmanager) -prediction -qq -sasl -silc -spell -tcl -tk -zephyr" 8,694 kB 
[ebuild  NS   ] dev-lang/python-2.4.4-r6  USE="berkdb gdbm ipv6 ncurses readline ssl -bootstrap -build -doc -examples -nocxx -nothreads -tk -ucs2" 10 kB 
[ebuild     U ] dev-lang/python-2.5.1-r3 [2.5.1-r2] USE="berkdb gdbm ipv6 ncurses readline sqlite ssl -bootstrap -build -doc -examples -nothreads -tk -ucs2" 0 kB 

Total: 3 packages (2 upgrades, 1 in new slot), Size of downloads: 8,703 kB