Thanks, I also found same thing before seeing your post, checked PPM, not available, then found and installed :
- python3-minimal_3.5.1-3_i386.deb
3.5.1-3 : python3-minimal : i386 : Xenial (16.04) : Ubuntu
Gave command "dpkg-buildpackage -b -d". It got past the stage where it has got stuck initially, but now it got stuck with Cx-Freez
... ... ...
building 'cx_Freeze.util' extension
creating build/temp.linux-i686-3.5
creating build/temp.linux-i686-3.5/source
i686-linux-gnu-gcc -pthread -DNDEBUG -g -fwrapv -O2 -Wall -Wstrict-prototypes -g -O2 -fPIC -I/root/piaware_builder/package-xenial/debian/venv/include -I/usr/include/python3.5m -c source/util.c -o build/temp.linux-i686-3.5/source/util.o
source/util.c:6:20: fatal error: Python.h: No such file or directory
compilation terminated.
error: command 'i686-linux-gnu-gcc' failed with exit status 1
debian/rules:60: recipe for target 'build_cxfreeze' failed
make[1]: *** [build_cxfreeze] Error 1
make[1]: Leaving directory '/root/piaware_builder/package-xenial'
debian/rules:88: recipe for target 'build' failed
make: *** [build] Error 2
dpkg-buildpackage: error: debian/rules build gave error exit status 2