the package libxml2 +python builds ok, but later module refresh fails:
$ spack module tcl refresh libxml2
==> You are about to regenerate tcl module files for:
-- linux-ubuntu16.04-x86_64 / gcc@7.4.0 -------------------------
tqifilo libxml2@2.9.8 e4joz6t libxml2@2.9.8
==> Do you want to proceed? [y/n] y
==> Regenerating tcl module files
==> Warning: Could not write module file [/usr/local/pkg/Modules/spack/modules/linux-ubuntu16.04-x86_64/libxml2/.2.9.8-gcc7.4.0-py3-e4joz6t]
==> Warning: --> global name 'site_packages_dir' is not defined <--
the package
libxml2 +pythonbuilds ok, but later module refresh fails: