The following steps are based on this post on the OE mailing list

The provided python-core and pyserial  packages can be installed but some dependencies are missing, namely the struct modules and a few other. This page explains how to rebuild and install properly compiled packages that will work. The following steps require the OpenEmbedded build environment to be properly installed and configured as explained here.

The following commands will do this:

download the correct python manifest file from here.

copy it over the existing manifest file in ~gumstix/gumstix-oe/org.openembedded.snapshot/packages/python

rebuild python package

send it over to the gumstix

remove any existing python packages

install the newly compiled one and pyserial

wget http://sourceforge.net/tracker/download.php?group_id=98784&atid=1013768&file_id=277435&aid=1916348 -O python-2.5-manifest.inc
cp ./python-2.5-manifest.inc ~/gumstix/gumstix-oe/org.openembedded.snapshot/packages/python
bitbake python (the original post says to use "-c rebuild" but th python build failed here because this option disable building dependencies)
scp ~/gumstix/gumstix-oe/tmp/deploy/glibc/ipk/armv5te/python-core_2.5.1-ml3_armv5te.ipk root@192.168.0.XXX:/media/card
ipkg remove libpython2.5-1.0 python-core -recursive
vi /var/lib/ipkg/base (looked for python-core and removed whole entry)
ipkg -d mmc install ./python-core_2.5.1-ml3_armv5te.ipk
ipkg-link add python-core
ipkg-link add libpython2.5-1.0
ipkg -d mmc install python-pyserial python-stringold python-threading python-datetime
ipkg-link add libssl0.9.7
ipkg-link add libcrypto0.9.7
ipkg-link add python-fcntl
ipkg-link add python-io
ipkg-link add python-math
ipkg-link add python-pyserial
ipkg-link add python-re
ipkg-link add python-stringold
ipkg-link add python-lang
ipkg-link add python-threading
ipkg-link add python-datetime
ipkg-link add python-codecs