path: root/cython.patch

diff --git .gitignore .gitignore
index 8f3f097..e6cdf4b 100644
--- .gitignore
+++ .gitignore
@@ -9,6 +9,6 @@ profile.out
 *.png
 *.vtk
 prof
+dist/
 docs/_build
-cython/cbecke.c
 pyquante2.egg-info/
diff --git MANIFEST.in MANIFEST.in
new file mode 100644
index 0000000..3547e38
--- /dev/null
+++ MANIFEST.in
@@ -0,0 +1,3 @@
+graft cython
+global-exclude *.html
+global-exclude *.py[cod]
diff --git cython/crys.c cython/crys.c
index bebed9e..c2e56cf 100644
--- cython/crys.c
+++ cython/crys.c
@@ -30,7 +30,10 @@
 #define M_PI 3.14159265358979323846
 #endif
 
-static double contr_coulomb(int lena,double *aexps,double *acoefs,double *anorms,
+static double roots[MAXROOTS],weights[MAXROOTS],G[MAXROOTS][MAXROOTS];
+static double B00,B1,B1p,C,Cp;
+
+double contr_coulomb(int lena,double *aexps,double *acoefs,double *anorms,
 		     double xa,double ya,double za,int la,int ma,int na,
 		     int lenb,double *bexps,double *bcoefs,double *bnorms,
 		     double xb,double yb,double zb,int lb,int mb,int nb,
@@ -52,7 +55,7 @@ static double contr_coulomb(int lena,double *aexps,double *acoefs,double *anorms
   return val;
 }
     
-static double coulomb_repulsion(double xa,double ya,double za,double norma,
+double coulomb_repulsion(double xa,double ya,double za,double norma,
 			 int la,int ma,int na,double alphaa,
 			 double xb,double yb,double zb,double normb,
 			 int lb,int mb,int nb,double alphab,
@@ -95,7 +98,7 @@ static double coulomb_repulsion(double xa,double ya,double za,double norma,
   return 2*sqrt(rho/M_PI)*norma*normb*normc*normd*sum; /* ABD eq 5 & 9 */
 }
 
-static void Roots(int n, double X){
+void Roots(int n, double X){
   if (n <= 3)
     Root123(n,X);
   else if (n==4) 
@@ -108,7 +111,7 @@ static void Roots(int n, double X){
 }
 
 
-static void Root123(int n, double X){
+void Root123(int n, double X){
 
   double R12, PIE4, R22, W22, R13, R23, W23, R33, W33;
   double RT1=0,RT2=0,RT3=0,WW1=0,WW2=0,WW3=0;
@@ -565,7 +568,7 @@ static void Root123(int n, double X){
   return;
 }
 
-static void Root4(double X){
+void Root4(double X){
   double R14,PIE4,R24,W24,R34,W34,R44,W44;
   double RT1=0,RT2=0,RT3=0,RT4=0,WW1=0,WW2=0,WW3=0,WW4=0;
   double Y,E;
@@ -931,7 +934,7 @@ static void Root4(double X){
   return;
 }
 
-static void Root5(double X){
+void Root5(double X){
   double R15,PIE4,R25,W25,R35,W35,R45,W45,R55,W55;
   double RT1=0,RT2=0,RT3=0,RT4=0,RT5=0,
     WW1=0,WW2=0,WW3=0,WW4=0,WW5=0;
@@ -1436,12 +1439,12 @@ static void Root5(double X){
   return;
 }
 
-static void Root6(int n,double X){
+void Root6(int n,double X){
   printf("crys.c:Root6 not implemented yet\n");
   return ;
 }
 
-static double Int1d(double t,int ix,int jx,int kx, int lx,
+double Int1d(double t,int ix,int jx,int kx, int lx,
 	     double xi,double xj, double xk,double xl,
 	     double alphai,double alphaj,double alphak,double alphal){
   double Ix;
@@ -1451,7 +1454,7 @@ static double Int1d(double t,int ix,int jx,int kx, int lx,
   return Ix;
 }
 
-static void RecurFactors(double t,double A,double B,
+void RecurFactors(double t,double A,double B,
 		  double Px,double Qx,double xi,double xk){
   /* ABD eqs 12-14 */
   double fff;
@@ -1464,7 +1467,7 @@ static void RecurFactors(double t,double A,double B,
   return;
 }
 
-static void RecurFactorsGamess(double t,double A,double B,
+void RecurFactorsGamess(double t,double A,double B,
 			double Px,double Qx,double xi,double xk){
   /* Analogous versions taken from Gamess source code */
   double fff;
@@ -1477,7 +1480,7 @@ static void RecurFactorsGamess(double t,double A,double B,
   return;
 }
 
-static void Recur(double t, int i, int j, int k, int l,
+void Recur(double t, int i, int j, int k, int l,
 	   double xi, double xj, double xk, double xl,
 	   double alphai, double alphaj, double alphak, double alphal){
   /* Form G(n,m)=I(n,0,m,0) intermediate values for a Rys polynomial */
@@ -1514,7 +1517,7 @@ static void Recur(double t, int i, int j, int k, int l,
     return;
 }
 
-static double Shift(int i, int j, int k, int l, double xij, double xkl){
+double Shift(int i, int j, int k, int l, double xij, double xkl){
   /* Compute and  output I(i,j,k,l) from I(i+j,0,k+l,0) (G) */
   /*  xij = xi-xj, xkl = xk-xl */
 
@@ -1532,19 +1535,18 @@ static double Shift(int i, int j, int k, int l, double xij, double xkl){
 }
 
 /* Util functions: */
-static double product_center_1D(double alphaa, double xa, 
+double product_center_1D(double alphaa, double xa, 
 			 double alphab, double xb){
   return (alphaa*xa+alphab*xb)/(alphaa+alphab);
 }
 
-static double dist2(double x1, double y1, double z1, double x2, double y2, double z2){
+double dist2(double x1, double y1, double z1, double x2, double y2, double z2){
   return (x1-x2)*(x1-x2)+(y1-y2)*(y1-y2)+(z1-z2)*(z1-z2);
 }
 
-static int binomial(int a, int b){return fact(a)/(fact(b)*fact(a-b));}
+int binomial(int a, int b){return fact(a)/(fact(b)*fact(a-b));}
 
-static int fact(int n){
+int fact(int n){
   if (n <= 1) return 1;
   return n*fact(n-1);
 }
-
diff --git cython/crys.h cython/crys.h
index 78832f4..0ffd954 100644
--- cython/crys.h
+++ cython/crys.h
@@ -10,10 +10,8 @@
  *
  **************************************************************************/
 #define MAXROOTS 20
-static double roots[MAXROOTS],weights[MAXROOTS],G[MAXROOTS][MAXROOTS];
-static double B00,B1,B1p,C,Cp;
 
-static double contr_coulomb(int lena,double *aexps,double *acoefs,double *anorms,
+double contr_coulomb(int lena,double *aexps,double *acoefs,double *anorms,
 		     double xa,double ya,double za,int la,int ma,int na,
 		     int lenb,double *bexps,double *bcoefs,double *bnorms,
 		     double xb,double yb,double zb,int lb,int mb,int nb,
@@ -22,7 +20,7 @@ static double contr_coulomb(int lena,double *aexps,double *acoefs,double *anorms
 		     int lend,double *dexps,double *dcoefs,double *dnorms,
 		     double xd,double yd,double zd,int ld,int md,int nd);
 
-static double coulomb_repulsion(double xa,double ya,double za,double norma,
+double coulomb_repulsion(double xa,double ya,double za,double norma,
 			 int la,int ma,int na,double alphaa,
 			 double xb,double yb,double zb,double normb,
 			 int lb,int mb,int nb,double alphab,
@@ -31,34 +29,33 @@ static double coulomb_repulsion(double xa,double ya,double za,double norma,
 			 double xd,double yd,double zd,double normd,
 			 int ld,int md,int nd,double alphad);
 
-static void Roots(int n, double X);
-static void Root123(int n, double X);
-static void Root4(double X);
-static void Root5(double X);
-static void Root6(int n,double X);
-static double Int1d(double t,int ix,int jx,int kx, int lx,
+void Roots(int n, double X);
+void Root123(int n, double X);
+void Root4(double X);
+void Root5(double X);
+void Root6(int n,double X);
+double Int1d(double t,int ix,int jx,int kx, int lx,
 	     double xi,double xj, double xk,double xl,
 	     double alphai,double alphaj,double alphak,double alphal);
 
-static void RecurFactors(double t,double A,double B,
+void RecurFactors(double t,double A,double B,
 		  double Px,double Qx,double xi,double xk);
 
-static void RecurFactorsGamess(double t,double A,double B,
+void RecurFactorsGamess(double t,double A,double B,
 			double Px,double Qx,double xi,double xk);
 
-static void Recur(double t, int i, int j, int k, int l,
+void Recur(double t, int i, int j, int k, int l,
 	   double xi, double xj, double xk, double xl,
 	   double alphai, double alphaj, double alphak, double alphal);
 
-static double Shift(int i, int j, int k, int l, double xij, double xkl);
+double Shift(int i, int j, int k, int l, double xij, double xkl);
 
-static double product_center_1D(double alphaa, double xa, 
+double product_center_1D(double alphaa, double xa, 
 				double alphab, double xb);
 
 // These look like duplicates. Have to figure out a better place to put
 // these in both the python and C versions:
-static double dist2(double x1, double y1, double z1, 
+double dist2(double x1, double y1, double z1, 
 		    double x2, double y2, double z2);
-static int binomial(int a, int b);
-static int fact(int n);
-
+int binomial(int a, int b);
+int fact(int n);
diff --git pyproject.toml pyproject.toml
index 51b2b11..c8a953b 100644
--- pyproject.toml
+++ pyproject.toml
@@ -1,5 +1,6 @@
 [build-system]
 requires = [
+    "cython>=3.0.11",
     "numpy",
     "setuptools>=61.0",
 ]
diff --git pyquante2/grid/grid.py pyquante2/grid/grid.py
index 2382a63..a0a5324 100644
--- pyquante2/grid/grid.py
+++ pyquante2/grid/grid.py
@@ -9,8 +9,9 @@ from pyquante2.grid.atomic_grid import atomic_grid
 
 try:
     from pyquante2.cbecke import becke_reweight_atoms
-except:
-    print("Couldn't find cython becke routine")
+except ImportError:
+    import sys
+    print("Couldn't find cython becke routine", file=sys.stderr)
     from pyquante2.grid.becke import becke_reweight_atoms
 
 
diff --git pyquante2/ints/integrals.py pyquante2/ints/integrals.py
index f56dd9d..ce1c1ac 100644
--- pyquante2/ints/integrals.py
+++ pyquante2/ints/integrals.py
@@ -4,13 +4,15 @@ General module for integral generation and access.
 try:
     from pyquante2.cints.hgp import ERI
 except:
-    print("Couldn't find cython int routine")
+    import sys
+    print("Couldn't find cython int routine", file=sys.stderr)
     from pyquante2.ints.hgp import ERI
 
 try:
     from pyquante2.cints.one import S,T,V
 except:
-    print("Couldn't find cython int routine")
+    import sys
+    print("Couldn't find cython int routine", file=sys.stderr)
     from pyquante2.ints.one import S,T,V
 
 from pyquante2.utils import pairs
diff --git setup.py setup.py
index aec62a1..99c35cb 100644
--- setup.py
+++ setup.py
@@ -1,52 +1,81 @@
+import os.path
+import sys
+from os import getenv
 from pathlib import Path
 from setuptools import setup
 from setuptools.extension import Extension
+from setuptools.command.build_ext import build_ext
+
+import numpy as np
+
+CYTHON_DISABLED = getenv("PYQUANTE_CYTHON_DISABLED", "False").lower() in (
+    "true",
+    "1",
+    "t",
+)
 
 try:
     from Cython.Build import cythonize
+
+    FILE_EXT = "pyx"
+    CYTHON_AVAILABLE = True
+    print("Cython available")
 except ImportError:
     FILE_EXT = "c"
-    USE_CYTHON = False
-else:
-    import numpy as np
+    CYTHON_AVAILABLE = False
+    print("Cython not available")
 
-    FILE_EXT = "pyx"
+if CYTHON_AVAILABLE and not CYTHON_DISABLED:
+    print("Cython available and requested")
     USE_CYTHON = True
+else:
+    USE_CYTHON = False
 
 
 _NUMPY_MACROS = [("NPY_NO_DEPRECATED_API", "NPY_1_7_API_VERSION")]
 ext_modules = [
     Extension(
         "pyquante2.cints.one",
-        [f"cython/cone_wrap.{FILE_EXT}", "cython/cints.c"],
+        [
+            os.path.join("cython", f"cone_wrap.{FILE_EXT}"),
+            os.path.join("cython", "cints.c"),
+        ],
         define_macros=_NUMPY_MACROS,
     ),
     Extension(
         "pyquante2.cints.two",
-        [f"cython/ctwo_wrap.{FILE_EXT}", "cython/cints.c"],
+        [
+            os.path.join("cython", f"ctwo_wrap.{FILE_EXT}"),
+            os.path.join("cython", "cints.c"),
+        ],
         define_macros=_NUMPY_MACROS,
     ),
     Extension(
         "pyquante2.cints.hgp",
-        [f"cython/chgp_wrap.{FILE_EXT}", "cython/chgp.c", "cython/cints.c"],
+        [
+            os.path.join("cython", f"chgp_wrap.{FILE_EXT}"),
+            os.path.join("cython", "chgp.c"),
+            os.path.join("cython", "cints.c"),
+        ],
         define_macros=_NUMPY_MACROS,
     ),
     Extension(
         "pyquante2.cints.rys",
-        [f"cython/crys_wrap.{FILE_EXT}", "cython/crys.c"],
+        [
+            os.path.join("cython", f"crys_wrap.{FILE_EXT}"),
+            os.path.join("cython", "crys.c"),
+        ],
         define_macros=_NUMPY_MACROS,
     ),
+    Extension(
+        "pyquante2.cbecke",
+        [os.path.join("cython", f"cbecke.{FILE_EXT}")],
+        define_macros=_NUMPY_MACROS,
+        include_dirs=[np.get_include()],
+    ),
 ]
 
 if USE_CYTHON:
-    ext_modules.append(
-        Extension(
-            "pyquante2.cbecke",
-            ["cython/cbecke.pyx"],
-            define_macros=_NUMPY_MACROS,
-            include_dirs=[np.get_include()],
-        )
-    )
     ext_modules = cythonize(ext_modules, annotate=True)
 
 # Make intermediate directories so that `setup.py build_ext -i` works.
@@ -56,7 +85,32 @@ for ext_module in ext_modules:
     path = _PWD.joinpath(*ext_module.name.split(".")[:-1])
     path.mkdir(parents=True, exist_ok=True)
 
+
+class optional_build_ext(build_ext):
+    """build_ext that allows installation to continue if Extensions can't be built.
+
+    This is useful for when there is code logic that will instead route to a
+    pure Python implementation.
+    """
+
+    def build_extension(self, ext):
+        self.couldnt_build = False
+        try:
+            super().build_extension(ext)
+        except:
+            self.couldnt_build = True
+            print(
+                "Couldn't compile extension, will fall back to pure Python implementations",
+                file=sys.stderr,
+            )
+
+    def copy_extensions_to_source(self):
+        if not self.couldnt_build:
+            super().copy_extensions_to_source()
+
+
 setup(
     name="pyquante2",
     ext_modules=ext_modules,
+    cmdclass={"build_ext": optional_build_ext},
 )