Steps to reproduce the issue

$ spack spec -I py-pygtk
Input spec
--------------------------------
 -   py-pygtk

Concretized
--------------------------------
==> Error: py-pygtk is unsatisfiable, errors are:
  no version satisfies the given constraints

    To see full clingo unsat cores, re-run with `spack --show-cores=full`
    For full, subset-minimal unsat cores, re-run with `spack --show-cores=minimized
    Warning: This may take (up to) hours for some specs

Information on your system

• Spack: 0.17.0-516-5319b6e3b1
• Python: 3.9.5
• Platform: linux-ubuntu21.04-sandybridge
• Concretizer: clingo

Additional information

No response

General information

• I have run spack debug report and reported the version of Spack/Python/Platform
• I have run spack maintainers <name-of-the-package> and @mentioned any maintainers
• I have uploaded the build log and environment files
• I have searched the issues of this repo and believe this is not a duplicate