$ spack install py-matplotlib@2.0.0
==> Error: An unsatisfiable dependency constraint has been detected for spec:

    py-pillow@3.2.0%gcc@7.1.1~freetype+jpeg~jpeg2000~lcms~tiff+zlib arch=linux-arch-x86_64 
        ^binutils@2.28%gcc@7.1.1+gold~libiberty~plugins arch=linux-arch-x86_64 
            ^bison@3.0.4%gcc@7.1.1 arch=linux-arch-x86_64 
                ^m4@1.4.18%gcc@7.1.1+sigsegv arch=linux-arch-x86_64 
                    ^libsigsegv
            ^flex@2.6.4%gcc@7.1.1+lex arch=linux-arch-x86_64 
                ^gettext@0.19.8.1%gcc@7.1.1+bzip2+curses+git~libunistring+libxml2+tar+xz arch=linux-arch-x86_64 
                    ^bzip2@1.0.6%gcc@7.1.1+shared arch=linux-arch-x86_64 
                    ^libxml2
                        ^pkg-config@0.29.2%gcc@7.1.1+internal_glib arch=linux-arch-x86_64 
                        ^xz
                        ^zlib@1.2.11%gcc@7.1.1+pic+shared arch=linux-arch-x86_64 
                    ^ncurses@6.0%gcc@7.1.1~symlinks arch=linux-arch-x86_64 
                    ^tar
                ^help2man@1.47.4%gcc@7.1.1 arch=linux-arch-x86_64 
        ^libjpeg-turbo@1.5.0%gcc@7.1.1 arch=linux-arch-x86_64 
            ^nasm
        ^py-setuptools@35.0.2%gcc@7.1.1 arch=linux-arch-x86_64 
            ^py-appdirs@1.4.3%gcc@7.1.1 arch=linux-arch-x86_64 
                ^python@2.7.13%gcc@7.1.1+shared~tk~ucs4 arch=linux-arch-x86_64 
                    ^openssl@1.0.2k%gcc@7.1.1 arch=linux-arch-x86_64 
                    ^readline@7.0%gcc@7.1.1 arch=linux-arch-x86_64 
                    ^sqlite@3.20.0%gcc@7.1.1 arch=linux-arch-x86_64 
            ^py-packaging@16.8%gcc@7.1.1 arch=linux-arch-x86_64 
                ^py-pyparsing@2.2.0%gcc@7.1.1 arch=linux-arch-x86_64 
                ^py-six@1.10.0%gcc@7.1.1 arch=linux-arch-x86_64 


while trying to concretize the partial spec:

    py-matplotlib@2.0.0%gcc@7.1.1~animation+image~ipython~latex~qt+tk arch=linux-arch-x86_64 
        ^freetype@2.7.1%gcc@7.1.1 arch=linux-arch-x86_64 
            ^bzip2@1.0.6%gcc@7.1.1+shared arch=linux-arch-x86_64 
            ^libpng@1.6.29%gcc@7.1.1 arch=linux-arch-x86_64 
                ^zlib@1.2.11%gcc@7.1.1+pic+shared arch=linux-arch-x86_64 
            ^pkg-config@0.29.2%gcc@7.1.1+internal_glib arch=linux-arch-x86_64 
        ^py-cycler@0.10.0%gcc@7.1.1 arch=linux-arch-x86_64 
            ^py-setuptools@35.0.2%gcc@7.1.1 arch=linux-arch-x86_64 
                ^py-appdirs@1.4.3%gcc@7.1.1 arch=linux-arch-x86_64 
                    ^python@2.7.13%gcc@7.1.1+shared~tk~ucs4 arch=linux-arch-x86_64 
                        ^ncurses@6.0%gcc@7.1.1~symlinks arch=linux-arch-x86_64 
                        ^openssl@1.0.2k%gcc@7.1.1 arch=linux-arch-x86_64 
                        ^readline@7.0%gcc@7.1.1 arch=linux-arch-x86_64 
                        ^sqlite@3.20.0%gcc@7.1.1 arch=linux-arch-x86_64 
                ^py-packaging@16.8%gcc@7.1.1 arch=linux-arch-x86_64 
                    ^py-pyparsing@2.2.0%gcc@7.1.1 arch=linux-arch-x86_64 
                    ^py-six@1.10.0%gcc@7.1.1 arch=linux-arch-x86_64 
        ^py-dateutil@2.5.2%gcc@7.1.1 arch=linux-arch-x86_64 
        ^py-functools32@3.2.3-2%gcc@7.1.1 arch=linux-arch-x86_64 
        ^py-numpy@1.13.1%gcc@7.1.1+blas+lapack arch=linux-arch-x86_64 
            ^openblas@0.2.20%gcc@7.1.1~openmp+pic+shared arch=linux-arch-x86_64 
        ^py-pillow@3.2.0%gcc@7.1.1~freetype+jpeg~jpeg2000~lcms~tiff+zlib arch=linux-arch-x86_64 
            ^binutils@2.28%gcc@7.1.1+gold~libiberty~plugins arch=linux-arch-x86_64 
                ^bison@3.0.4%gcc@7.1.1 arch=linux-arch-x86_64 
                    ^m4@1.4.18%gcc@7.1.1+sigsegv arch=linux-arch-x86_64 
                        ^libsigsegv
                ^flex@2.6.4%gcc@7.1.1+lex arch=linux-arch-x86_64 
                    ^gettext@0.19.8.1%gcc@7.1.1+bzip2+curses+git~libunistring+libxml2+tar+xz arch=linux-arch-x86_64 
                        ^libxml2
                            ^xz
                        ^tar
                    ^help2man@1.47.4%gcc@7.1.1 arch=linux-arch-x86_64 
            ^libjpeg-turbo@1.5.0%gcc@7.1.1 arch=linux-arch-x86_64 
                ^nasm
        ^py-pytz@2017.2%gcc@7.1.1 arch=linux-arch-x86_64 
        ^py-subprocess32@3.2.7%gcc@7.1.1 arch=linux-arch-x86_64 
        ^qhull@2015.2%gcc@7.1.1 build_type=RelWithDebInfo arch=linux-arch-x86_64 
            ^cmake@3.9.0%gcc@7.1.1~doc+ncurses+openssl+ownlibs~qt arch=linux-arch-x86_64 
        ^tk@8.6.6%gcc@7.1.1 arch=linux-arch-x86_64 
            ^libx11@1.6.5%gcc@7.1.1 arch=linux-arch-x86_64 
                ^inputproto@2.3.2%gcc@7.1.1 arch=linux-arch-x86_64 
                    ^util-macros@1.19.1%gcc@7.1.1 arch=linux-arch-x86_64 
                ^kbproto@1.0.7%gcc@7.1.1 arch=linux-arch-x86_64 
                ^libxcb@1.12%gcc@7.1.1 arch=linux-arch-x86_64 
                    ^libpthread-stubs@0.4%gcc@7.1.1 arch=linux-arch-x86_64 
                    ^libxau@1.0.8%gcc@7.1.1 arch=linux-arch-x86_64 
                        ^xproto@7.0.31%gcc@7.1.1 arch=linux-arch-x86_64 
                    ^libxdmcp@1.1.2%gcc@7.1.1 arch=linux-arch-x86_64 
                    ^xcb-proto@1.12%gcc@7.1.1 arch=linux-arch-x86_64 
                ^xextproto@7.3.0%gcc@7.1.1 arch=linux-arch-x86_64 
                ^xtrans@1.3.5%gcc@7.1.1 arch=linux-arch-x86_64 
            ^tcl@8.6.6%gcc@7.1.1 arch=linux-arch-x86_64 


py-matplotlib requires py-pillow dependency py-pillow@3.2.0%gcc@7.1.1~freetype+jpeg~jpeg2000~lcms~tiff+zlib arch=linux-arch-x86_64 ^binutils@2.28%gcc@7.1.1+gold~libiberty~plugins arch=linux-arch-x86_64 ^bison@3.0.4%gcc@7.1.1 arch=linux-arch-x86_64 ^bzip2@1.0.6%gcc@7.1.1+shared arch=linux-arch-x86_64 ^flex@2.6.4%gcc@7.1.1+lex arch=linux-arch-x86_64 ^gettext@0.19.8.1%gcc@7.1.1+bzip2+curses+git~libunistring+libxml2+tar+xz arch=linux-arch-x86_64 ^help2man@1.47.4%gcc@7.1.1 arch=linux-arch-x86_64 ^libjpeg-turbo@1.5.0%gcc@7.1.1 arch=linux-arch-x86_64 ^libsigsegv^libxml2^m4@1.4.18%gcc@7.1.1+sigsegv arch=linux-arch-x86_64 ^nasm^ncurses@6.0%gcc@7.1.1~symlinks arch=linux-arch-x86_64 ^openssl@1.0.2k%gcc@7.1.1 arch=linux-arch-x86_64 ^pkg-config@0.29.2%gcc@7.1.1+internal_glib arch=linux-arch-x86_64 ^py-appdirs@1.4.3%gcc@7.1.1 arch=linux-arch-x86_64 ^py-packaging@16.8%gcc@7.1.1 arch=linux-arch-x86_64 ^py-pyparsing@2.2.0%gcc@7.1.1 arch=linux-arch-x86_64 ^py-setuptools@35.0.2%gcc@7.1.1 arch=linux-arch-x86_64 ^py-six@1.10.0%gcc@7.1.1 arch=linux-arch-x86_64 ^python@2.7.13%gcc@7.1.1+shared~tk~ucs4 arch=linux-arch-x86_64 ^readline@7.0%gcc@7.1.1 arch=linux-arch-x86_64 ^sqlite@3.20.0%gcc@7.1.1 arch=linux-arch-x86_64 ^tar^xz^zlib@1.2.11%gcc@7.1.1+pic+shared arch=linux-arch-x86_64, but spec asked for py-pillow@3.2.0%gcc@7.1.1~freetype+jpeg~jpeg2000~lcms~tiff+zlib arch=linux-arch-x86_64 ^binutils@2.28%gcc@7.1.1+gold~libiberty~plugins arch=linux-arch-x86_64 ^bison@3.0.4%gcc@7.1.1 arch=linux-arch-x86_64 ^bzip2@1.0.6%gcc@7.1.1+shared arch=linux-arch-x86_64 ^flex@2.6.4%gcc@7.1.1+lex arch=linux-arch-x86_64 ^gettext@0.19.8.1%gcc@7.1.1+bzip2+curses+git~libunistring+libxml2+tar+xz arch=linux-arch-x86_64 ^help2man@1.47.4%gcc@7.1.1 arch=linux-arch-x86_64 ^libjpeg-turbo@1.5.0%gcc@7.1.1 arch=linux-arch-x86_64 ^libsigsegv^libxml2^m4@1.4.18%gcc@7.1.1+sigsegv arch=linux-arch-x86_64 ^nasm^ncurses@6.0%gcc@7.1.1~symlinks arch=linux-arch-x86_64 ^openssl@1.0.2k%gcc@7.1.1 arch=linux-arch-x86_64 ^pkg-config@0.29.2%gcc@7.1.1+internal_glib arch=linux-arch-x86_64 ^py-appdirs@1.4.3%gcc@7.1.1 arch=linux-arch-x86_64 ^py-packaging@16.8%gcc@7.1.1 arch=linux-arch-x86_64 ^py-pyparsing@2.2.0%gcc@7.1.1 arch=linux-arch-x86_64 ^py-setuptools@35.0.2%gcc@7.1.1 arch=linux-arch-x86_64 ^py-six@1.10.0%gcc@7.1.1 arch=linux-arch-x86_64 ^python@2.7.13%gcc@7.1.1+shared~tk~ucs4 arch=linux-arch-x86_64 ^readline@7.0%gcc@7.1.1 arch=linux-arch-x86_64 ^sqlite@3.20.0%gcc@7.1.1 arch=linux-arch-x86_64 ^tar^xz^zlib@1.2.11%gcc@7.1.1+pic+shared arch=linux-arch-x86_64