Add option for Python only install (#72)

* Add option for Python only install

* Update changelog

CHANGELOG.rst

@@ -18,11 +18,13 @@
 
 - Improvements:
 
-  - Add ``fall_back_on_python`` boolean keyword argument to
+  - Added ``fall_back_on_python`` boolean keyword argument to
     ``ForceConstants.calculate_qpoint_phonon_modes`` to control
     whether the Python implementation is used as a fallback to the C
     extension or not, see
     `#35 <https://github.com/pace-neutrons/Euphonic/issues/35>`_
+  - Added ``--python-only`` option to ``setup.py`` to enable install
+    without the C extension
 
 - Bug fixes:
 

doc/source/index.rst

@@ -56,18 +56,14 @@ If you don't require plotting or reading of Phonopy files, just use:
 
   pip install .
 
-Installing the C extension (optional)
-=====================================
-Euphonic has an optional C extension, which can lead to increased performance
-and enable use of multiple cores when interpolating phonons. By default
-Euphonic will attempt to install this extension, but will print a warning and
-fall back to the pure Python version if this fails. To determine if the C
-extension is installing properly and investigate any problems, it is best to
-increase pip's verbosity:
+Installing the C extension
+==========================
 
-.. code-block:: bash
-
-  pip install -vvv euphonic
+By default, Euphonic will attempt to build and install the C extension,
+which can lead to increased performance and enable use of multiple cores when
+interpolating phonons. See below for information on installing the extension
+for different platforms. If you are having trouble installing the C extension
+and don't require it, see `Installing Euphonic without the C extension`_
 
 **Windows**
 
@@ -94,6 +90,21 @@ before running pip install run:
 
   brew install llvm
 
+Installing Euphonic without the C extension
+===========================================
+
+If you don't need the extra performance the C extension provides, you can
+install the Python parts only with:
+
+.. code-block:: bash
+
+  pip install --install-option="--python-only" euphonic
+
+Note that using this option disables the use of wheels which, if they haven't
+been installed already, actually makes installing other packages such as Numpy
+more difficult. The easiest way around this is running the usual install
+command first (which will install all the dependencies), then running again
+with the ``--install-option="--python-only"`` option.
 
 .. toctree::
    :hidden:

setup.py

@@ -1,50 +1,63 @@
 import versioneer
 try:
     from setuptools import setup, find_packages, Extension
+    from setuptools.command.install import install
 except ImportError:
     from distutils.core import setup, find_packages, Extension
+    from distutils.command.install import install
 
 
-def run_setup(build_c=True):
+class InstallCommand(install):
+    user_options = install.user_options + [('python-only', None, 'Install only Python')]
+
+    def initialize_options(self):
+        install.initialize_options(self)
+        self.python_only = 0
+
+    def finalize_options(self):
+        install.finalize_options(self)
+        if not bool(self.python_only):
+            self.distribution.ext_modules = [get_c_extension()]
 
-    if build_c:
-        import os
-        import numpy as np
-        from sys import platform
-        import subprocess
-        include_dirs = [np.get_include(), 'c']
-        sources = ['c/_euphonic.c', 'c/dyn_mat.c', 'c/util.c', 'c/py_util.c',
-                   'c/load_libs.c']
-        if platform == 'win32':
-            # Windows - assume MSVC compiler
-            compile_args = ['/openmp']
-            link_args = None
-        elif platform == 'darwin':
-            # OSX - assume brew install llvm
-            brew_prefix_cmd_return = subprocess.run(["brew", "--prefix"],
-                                                    stdout=subprocess.PIPE)
-            brew_prefix = brew_prefix_cmd_return.stdout.decode("utf-8").strip()
-            os.environ['CC'] = '{}/opt/llvm/bin/clang'.format(brew_prefix)
-            compile_args = ['-fopenmp']
-            link_args = ['-L{}/opt/llvm/lib'.format(brew_prefix), '-fopenmp']
-        else:
-            # Linux - assume gcc
-            os.environ['CC'] = 'gcc'
-            compile_args = ['-fopenmp']
-            link_args = ['-fopenmp']
 
-        euphonic_extension = Extension(
-            'euphonic._euphonic',
-            extra_compile_args=compile_args,
-            extra_link_args=link_args,
-            include_dirs=include_dirs,
-            sources=sources
-        )
-        ext_modules = [euphonic_extension]
+def get_c_extension():
+    import os
+    import numpy as np
+    from sys import platform
+    import subprocess
+    include_dirs = [np.get_include(), 'c']
+    sources = ['c/_euphonic.c', 'c/dyn_mat.c', 'c/util.c', 'c/py_util.c',
+               'c/load_libs.c']
+    if platform == 'win32':
+        # Windows - assume MSVC compiler
+        compile_args = ['/openmp']
+        link_args = None
+    elif platform == 'darwin':
+        # OSX - assume brew install llvm
+        brew_prefix_cmd_return = subprocess.run(["brew", "--prefix"],
+                                                stdout=subprocess.PIPE)
+        brew_prefix = brew_prefix_cmd_return.stdout.decode("utf-8").strip()
+        os.environ['CC'] = '{}/opt/llvm/bin/clang'.format(brew_prefix)
+        compile_args = ['-fopenmp']
+        link_args = ['-L{}/opt/llvm/lib'.format(brew_prefix), '-fopenmp']
     else:
-        ext_modules = None
+        # Linux - assume gcc
+        os.environ['CC'] = 'gcc'
+        compile_args = ['-fopenmp']
+        link_args = ['-fopenmp']
+
+    euphonic_c_extension = Extension(
+        'euphonic._euphonic',
+        extra_compile_args=compile_args,
+        extra_link_args=link_args,
+        include_dirs=include_dirs,
+        sources=sources
+    )
+    return euphonic_c_extension
 
 
+def run_setup(build_c=True):
+
     with open('README.rst', 'r') as f:
         long_description = f.read()
 
@@ -55,10 +68,13 @@ def run_setup(build_c=True):
                'scripts/dos.py',
                'scripts/optimise_eta.py']
 
+    cmdclass = versioneer.get_cmdclass()
+    cmdclass['install'] = InstallCommand
+
     setup(
         name='euphonic',
         version=versioneer.get_version(),
-        cmdclass=versioneer.get_cmdclass(),
+        cmdclass=cmdclass,
         author='Rebecca Fair',
         author_email='[email protected]',
         description=(
@@ -79,17 +95,7 @@ def run_setup(build_c=True):
             'matplotlib': ['matplotlib>=1.4.2'],
             'phonopy_reader': ['h5py>=2.9.0', 'PyYAML>=5.1.2']
         },
-        scripts=scripts,
-        ext_modules=ext_modules
+        scripts=scripts
     )
 
-
-try:
-    run_setup()
-except:
-    print('*'*79)
-    print(('Failed to build Euphonic C extension, installing pure '
-           'Python version instead'))
-    print('*'*79)
-    print("Unexpected error: {}".format(sys.exc_info()[0]))
-    run_setup(build_c=False)
+run_setup()