New packages: py-pymc3 and py-arviz (#15226)

This PR adds py-pymc3 and py-arviz as a dependency.

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

+# Copyright 2013-2020 Lawrence Livermore National Security, LLC and other
+# Spack Project Developers. See the top-level COPYRIGHT file for details.
+#
+# SPDX-License-Identifier: (Apache-2.0 OR MIT)
+
+from spack import *
+
+
+class PyArviz(PythonPackage):
+    """ArviZ (pronounced "AR-vees") is a Python package for exploratory
+    analysis of Bayesian models. Includes functions for posterior analysis,
+    model checking, comparison and diagnostics."""
+
+    homepage = "http://github.com/arviz-devs/arviz"
+    url      = "https://pypi.io/packages/source/a/arviz/arviz-0.6.1.tar.gz"
+
+    version('0.6.1', sha256='435edf8db49c41a8fa198f959e7581063006c49a4efdef4755bb778db6fd4f72')
+
+    depends_on('py-setuptools', type='build')
+    depends_on('py-matplotlib@3.0:', type=('build', 'run'))
+    depends_on('py-numpy@1.12:', type=('build', 'run'))
+    depends_on('py-scipy@0.19:', type=('build', 'run'))
+    depends_on('py-packaging', type=('build', 'run'))
+    depends_on('py-pandas@0.23:', type=('build', 'run'))
+    depends_on('py-xarray@0.11:', type=('build', 'run'))
+    depends_on('py-netcdf4', type=('build', 'run'))

var/spack/repos/builtin/packages/py-pymc3/package.py

+# Copyright 2013-2020 Lawrence Livermore National Security, LLC and other
+# Spack Project Developers. See the top-level COPYRIGHT file for details.
+#
+# SPDX-License-Identifier: (Apache-2.0 OR MIT)
+
+from spack import *
+
+
+class PyPymc3(PythonPackage):
+    """PyMC3 is a Python package for Bayesian statistical modeling and
+    Probabilistic Machine Learning focusing on advanced Markov chain Monte
+    Carlo (MCMC) and variational inference (VI) algorithms. Its flexibility and
+    extensibility make it applicable to a large suite of problems."""
+
+    homepage = "http://github.com/pymc-devs/pymc3"
+    url      = "https://pypi.io/packages/source/p/pymc3/pymc3-3.8.tar.gz"
+
+    version('3.8', sha256='1bb2915e4a29877c681ead13932b0b7d276f7f496e9c3f09ba96b977c99caf00')
+
+    depends_on('python@3.5.4:', type=('build', 'run'))
+    depends_on('py-setuptools', type='build')
+    depends_on('py-arviz@0.4.1:', type=('build', 'run'))
+    depends_on('py-theano@1.0.4:', type=('build', 'run'))
+    depends_on('py-numpy@1.13.0:', type=('build', 'run'))
+    depends_on('py-scipy@0.18.1:', type=('build', 'run'))
+    depends_on('py-pandas@0.18.0:', type=('build', 'run'))
+    depends_on('py-patsy@0.4.0:', type=('build', 'run'))
+    depends_on('py-tqdm@4.8.4:', type=('build', 'run'))
+    depends_on('py-h5py@2.7.0:', type=('build', 'run'))