py-gpy: added +plotting variant (#42588)

Co-authored-by: Alex C Leute <aclrc@rit.edu>

var/spack/repos/builtin/packages/py-gpy/package.py

@@ -19,6 +19,8 @@ class PyGpy(PythonPackage):
     version("1.9.9", sha256="04faf0c24eacc4dea60727c50a48a07ddf9b5751a3b73c382105e2a31657c7ed")
     version("0.8.8", sha256="e135d928cf170e2ec7fb058a035b5a7e334dc6b84d0bfb981556782528341988")
 
+    variant("plotting", default=False, description="Enable plotting")
+
     depends_on("py-setuptools", type="build")
     depends_on("py-numpy@1.7:", type=("build", "run"))
     depends_on("py-scipy@0.16:", type=("build", "run"))
@@ -28,6 +30,10 @@ class PyGpy(PythonPackage):
     # cython is install_requires, but not used at runtime, so stick to build type
     depends_on("py-cython@0.29:", type="build")
 
+    with when("+plotting"):
+        depends_on("py-matplotlib@3.0:", type=("build", "run"))
+        depends_on("py-plotly@1.8.6:", type=("build", "run"))
+
     @run_before("install")
     def touch_sources(self):
         # This packages uses deprecated build_ext, for which we cannot