BLD: find Python.h when build_ext --include-dirs is set

Ensure that build_ext.include_dirs is the same physical list as
build_ext.distribution.include_dirs.

1 files changed, 17 insertions, 3 deletions

diff --git a/numpy/distutils/command/build_ext.py b/numpy/distutils/command/build_ext.py
index 59c453607..c588204e5 100644
--- a/numpy/distutils/command/build_ext.py
+++ b/numpy/distutils/command/build_ext.py
@@ -54,10 +54,24 @@ class build_ext (old_build_ext):
                 self.jobs = int(self.jobs)
             except ValueError:
                 raise ValueError("--jobs/-j argument must be an integer")
-        incl_dirs = self.include_dirs
+
+        # Ensure that self.include_dirs and self.distribution.include_dirs
+        # refer to the same list object. finalize_options will modify
+        # self.include_dirs, but self.distribution.include_dirs is used
+        # during the actual build.
+        # self.include_dirs is None unless paths are specified with
+        # --include-dirs.
+        # The include paths will be passed to the compiler in the order:
+        # numpy paths, --include-dirs paths, Python include path.
+        if isinstance(self.include_dirs, str):
+            self.include_dirs = self.include_dirs.split(os.pathsep)
+        incl_dirs = self.include_dirs or []
+        if self.distribution.include_dirs is None:
+            self.distribution.include_dirs = []
+        self.include_dirs = self.distribution.include_dirs
+        self.include_dirs.extend(incl_dirs)
+
         old_build_ext.finalize_options(self)
-        if incl_dirs is not None:
-            self.include_dirs.extend(self.distribution.include_dirs or [])
         self.set_undefined_options('build', ('jobs', 'jobs'))
 
     def run(self):