Couldt find Python headers

Trying to install avahi: prt-get depinst --install-scripts avahi and keep getting the message about python extensions not found, then the installation fails. checking for python script directory... ${prefix}/share/python2.5/site-packages checking for python extension module directory... ${exec_prefix}/lib/python2.5/site-packages checking for headers required to compile python extensions... not found Python 2.5 is installed successfully. Am I missing the point? Alexei