* Remove variants disabling blas and lapack for py-numpy, issues
building these have been resolved
* For CMake greater than 3.10, FindMPI changed, so use
MPIEXE_EXECUTABLE instead of MPIEXE for 3.10 and newer
* optional path to use spacks py-site-pkgs, install host-cfg for provenance
* add more comments and address review requests
* only use st-pkgs-dir when +python
* ascent does not need doxygen
* capture mpiexec if it exists
* added missing import
* flake8 fix
* default adios variant to False
* ascent develop now reqs conduit master
* optional path to use spacks py-site-pkgs, install host-cfg for provenance
* add more comments and address review requests
* only use st-pkgs-dir when +python
* ascent does not need doxygen
* capture mpiexec if it exists
* added missing import
* flake8 fix
* default adios variant to False
* ascent develop now reqs conduit master
* conduit: use hdf5 1.8 for wider output compat
* add ascent package and and deps
* proper use of site_packages_dir prop
* flake8
* add maitain, small updates
* flake8
* flake8
* fixs for docstrings for sphinx
## Motivation
Python installations are both important and unfortunately inconsistent. Depending on the Python version, OS, and the strength of the Earth's magnetic field when it was installed, the name of the Python executable, directory containing its libraries, library names, and the directory containing its headers can vary drastically.
I originally got into this mess with #3274, where I discovered that Boost could not be built with Python 3 because the executable is called `python3` and we were telling it to use `python`. I got deeper into this mess when I started hacking on #3140, where I discovered just how difficult it is to find the location and name of the Python libraries and headers.
Currently, half of the packages that depend on Python and need to know this information jump through hoops to determine the correct information. The other half are hard-coded to use `python`, `spec['python'].prefix.lib`, and `spec['python'].prefix.include`. Obviously, none of these packages would work for Python 3, and there's no reason to duplicate the effort. The Python package itself should contain all of the information necessary to use it properly. This is in line with the recent work by @alalazo and @davydden with respect to `spec['blas'].libs` and friends.
## Prefix
For most packages in Spack, we assume that the installation directory is `spec['python'].prefix`. This generally works for anything installed with Spack, but gets complicated when we include external packages. Python is a commonly used external package (it needs to be installed just to run Spack). If it was installed with Homebrew, `which python` would return `/usr/local/bin/python`, and most users would erroneously assume that `/usr/local` is the installation directory. If you peruse through #2173, you'll immediately see why this is not the case. Homebrew actually installs Python in `/usr/local/Cellar/python/2.7.12_2` and symlinks the executable to `/usr/local/bin/python`. `PYTHONHOME` (and presumably most things that need to know where Python is installed) needs to be set to the actual installation directory, not `/usr/local`.
Normally I would say, "sounds like user error, make sure to use the real installation directory in your `packages.yaml`". But I think we can make a special case for Python. That's what we decided in #2173 anyway. If we change our minds, I would be more than happy to simplify things.
To solve this problem, I created a `spec['python'].home` attribute that works the same way as `spec['python'].prefix` but queries Python to figure out where it was actually installed. @tgamblin Is there any way to overwrite `spec['python'].prefix`? I think it's currently immutable.
## Command
In general, Python 2 comes with both `python` and `python2` commands, while Python 3 only comes with a `python3` command. But this is up to the OS developers. For example, `/usr/bin/python` on Gentoo is actually Python 3. Worse yet, if someone is using an externally installed Python, all 3 commands may exist in the same directory! Here's what I'm thinking:
If the spec is for Python 3, try searching for the `python3` command.
If the spec is for Python 2, try searching for the `python2` command.
If neither are found, try searching for the `python` command.
## Libraries
Spack installs Python libraries in `spec['python'].prefix.lib`. Except on openSUSE 13, where it installs to `spec['python'].prefix.lib64` (see #2295 and #2253). On my CentOS 6 machine, the Python libraries are installed in `/usr/lib64`. Both need to work.
The libraries themselves change name depending on OS and Python version. For Python 2.7 on macOS, I'm seeing:
```
lib/libpython2.7.dylib
```
For Python 3.6 on CentOS 6, I'm seeing:
```
lib/libpython3.so
lib/libpython3.6m.so.1.0
lib/libpython3.6m.so -> lib/libpython3.6m.so.1.0
```
Notice the `m` after the version number. Yeah, that's a thing.
## Headers
In Python 2.7, I'm seeing:
```
include/python2.7/pyconfig.h
```
In Python 3.6, I'm seeing:
```
include/python3.6m/pyconfig.h
```
It looks like all Python 3 installations have this `m`. Tested with Python 3.2 and 3.6 on macOS and CentOS 6
Spack has really nice support for libraries (`find_libraries` and `LibraryList`), but nothing for headers. Fixed.
* add package for conduit
* try to fix main conduit docstring
* use join_path instead of pjoin
* address a few requests in pr #2670
change name of 'github-master' to 'master'
change 'docs' variant to 'doc', set default to False
remove explicit +shared variant spec for silo and hdf5 deps
(in the conduit +shared case) cases since they default to True
add reference to static rpath issue
(https://github.com/LLNL/spack/issues/2658)
* address pr #2670 requests
add todos and more info on why variants for deps where selected
use python module install python to enable spack activate
use .format instead of %s
