Improve setup.py to pip install numpy unless it's not yet installed.

python/pyproject.toml

@@ -0,0 +1,2 @@
+[build-system]
+requires = ["setuptools", "wheel", "numpy"]

python/setup.py

@@ -1,34 +1,24 @@
 import os
 import sys
+import sysconfig
+
 
 setup_type = sys.argv[1]
 
 try:
     from setuptools import setup, Extension
-    from setuptools.command.build_ext import build_ext as _build_ext
+    from setuptools.command.build_ext import build_ext
     use_setuptools = True
+    print("setuptools is used.")
 
-    class build_ext(_build_ext):
-        def finalize_options(self):
-            _build_ext.finalize_options(self)
-            # Prevent numpy from thinking it is still in its setup process:
-            if sys.version_info[0] >= 3:
-                import builtins
-                if hasattr(builtins, '__NUMPY_SETUP__'):
-                    del builtins.__NUMPY_SETUP__
-                import importlib
-                import numpy
-                importlib.reload(numpy)
-
-            else:
-                import __builtin__
-                if hasattr(__builtin__, '__NUMPY_SETUP__'):
-                    del __builtin__.__NUMPY_SETUP__
-                import imp
-                import numpy
-                imp.reload(numpy)
+    # Trick to pip install numpy when it's not installed.
+    # Reference: https://stackoverflow.com/questions/2379898/
+    class CustomBuildExtCommand(build_ext):
+        def run(self):
+            import numpy
             self.include_dirs.append(numpy.get_include())
-    print("setuptools is used.")
+            build_ext.run(self)
+
 except ImportError:
     from distutils.core import setup, Extension
     use_setuptools = False
@@ -42,7 +32,6 @@ def finalize_options(self):
         sys.exit(1)
 
 # Workaround Python issue 21121
-import sysconfig
 config_var = sysconfig.get_config_var("CFLAGS")
 if (config_var is not None and
     "-Werror=declaration-after-statement" in config_var):
@@ -85,7 +74,7 @@ def finalize_options(self):
 
 extra_compile_args = []
 if setup_type == 'test':
-   extra_compile_args.append("-UNDEBUG")
+    extra_compile_args.append("-UNDEBUG")
 extra_link_args = []
 define_macros = []
 
@@ -121,7 +110,8 @@ def finalize_options(self):
                 break
         except ValueError:
             nanoversion = 0
-version_nums.append(nanoversion)
+if nanoversion != 0:
+    version_nums.append(nanoversion)
 
 if None in version_nums:
     print("Failed to get version number in setup.py.")
@@ -133,7 +123,7 @@ def finalize_options(self):
 if use_setuptools:
     setup(name='spglib',
           version=version,
-          cmdclass={'build_ext': build_ext},
+          cmdclass={'build_ext': CustomBuildExtCommand},
           setup_requires=['numpy', 'setuptools>=18.0'],
           license='BSD-3-Clause',
           description='This is the spglib module.',
@@ -143,12 +133,12 @@ def finalize_options(self):
           author_email='atz.togo@gmail.com',
           url='http://atztogo.github.io/spglib/',
           packages=['spglib'],
-          install_requires=['numpy'],
+          install_requires=['numpy', ],
           provides=['spglib'],
           platforms=['all'],
           ext_modules=[extension],
           test_suite='nose.collector',
-          tests_require=['nose'])
+          tests_require=['nose', 'pyyaml'])
 else:
     setup(name='spglib',
           version=version,
@@ -165,4 +155,4 @@ def finalize_options(self):
           platforms=['all'],
           ext_modules=[extension],
           test_suite='nose.collector',
-          tests_require=['nose'])
+          tests_require=['nose', 'pyyaml'])