remove compatibility for compiling LAMMPS with Python 2.x and Python 3.5 and older

lib/python/Makefile.lammps.python2

@@ -1,7 +0,0 @@
-# Settings that the LAMMPS build will import when this package library is used
-# See the README file for more explanation
-
-python_SYSINC = $(shell which python2-config > /dev/null 2>&1 && python2-config --includes || (which python-config > /dev/null 2>&1 && python-config --includes || :))
-python_SYSLIB = $(shell which python2-config > /dev/null 2>&1 && python2-config --ldflags || (which python-config > /dev/null 2>&1 && python-config --ldflags || :))
-python_SYSPATH =
-PYTHON=$(shell which python2 > /dev/null 2>&1 && echo python2 || echo python)

lib/python/README

@@ -9,30 +9,29 @@ installation. If needed, you can copy one of the other provided
 Makefile.lammps.* files to to Makefile.lammps before building
 LAMMPS itself.
 
-The files Makefile.lammps.python2 and Makefile.lammps.python3 are
+The file Makefile.lammps.python3 is similar to the default file, but
-similar to the default file, but meant for the case that both,
+meant for the case that both, python 2 and python 3, are installed
-python 2 and python 3, are installed simultaneously and you want
+simultaneously.  LAMMPS only supports python 3.  If neither of these
-to prefer one over the other. If neither of these files work, you
+files work, you may have to create a custom Makefile.lammps file
-may have to create a custom Makefile.lammps file suitable for
+suitable for the version of Python on your system.  To illustrate, these
-the version of Python on your system.  To illustrate, these are
+are example settings from the Makefile.lammps.python3.13 file:
-example settings from the Makefile.lammps.python2.7 file:
 
-python_SYSINC = -I/usr/local/include/python2.7
+python_SYSINC = -I/usr/local/include/python3.13
-python_SYSLIB = -lpython2.7 -lnsl -ldl -lreadline -ltermcap -lpthread -lutil -lm
+python_SYSLIB = -lpython3.13 -ldl  -lm
-python_SYSPATH =
+python_SYSPATH = -L/usr/lib64
-PYTHON=python2.7
+PYTHON=python3.13
 
 python_SYSINC refers to the directory where Python's Python.h file is
 found.  LAMMPS includes this file.
 
 python_SYSLIB refers to the libraries needed to link to from an
 application (LAMMPS in this case) to "embed" Python in the
-application.  The Python library itself is listed (-lpython2.7) are
+application.  The Python library itself is listed (-lpython3.13) are
 are several system libraries needed by Python.
 
 python_SYSPATH refers to the path (e.g. -L/usr/local/lib) where the
 Python library can be found.  You may not need this setting if the
-path is already included in your LD_LIBRARY_PATH environment variable.
+path is already included in your LIBRARY_PATH environment variable.
 
 PYTHON is the name of the python interpreter. It is used for
 installing the LAMMPS python module with "make install-python"
@@ -45,7 +44,7 @@ run in embedded mode on your machine.
 
 Here is what this Python doc page says about it:
 
-https://docs.python.org/2/extending/embedding.html#compiling-and-linking-under-unix-like-systems
+https://docs.python.org/3/extending/embedding.html#compiling-and-linking-under-unix-like-systems
 
 "It is not necessarily trivial to find the right flags to pass to your
 compiler (and linker) in order to embed the Python interpreter into

src/KOKKOS/mliap_model_python_kokkos.cpp

@@ -68,12 +68,12 @@ MLIAPModelPythonKokkos<DeviceType>::MLIAPModelPythonKokkos(LAMMPS *lmp, char *co
   // Recipe from lammps/src/pair_python.cpp :
   // add current directory to PYTHONPATH
   PyObject *py_path = PySys_GetObject((char *) "path");
-  PyList_Append(py_path, PY_STRING_FROM_STRING("."));
+  PyList_Append(py_path, PyUnicode_FromString("."));
 
   // if LAMMPS_POTENTIALS environment variable is set, add it to PYTHONPATH as well
   const char *potentials_path = getenv("LAMMPS_POTENTIALS");
   if (potentials_path != nullptr) {
-    PyList_Append(py_path, PY_STRING_FROM_STRING(potentials_path));
+    PyList_Append(py_path, PyUnicode_FromString(potentials_path));
   }
   PyGILState_Release(gstate);
   if (coefffilename) read_coeffs(coefffilename);

src/ML-IAP/mliap_model_python.cpp

@@ -62,12 +62,12 @@ MLIAPModelPython::MLIAPModelPython(LAMMPS *lmp, char *coefffilename, bool is_chi
   // Recipe from lammps/src/pair_python.cpp :
   // add current directory to PYTHONPATH
   PyObject *py_path = PySys_GetObject((char *) "path");
-  PyList_Append(py_path, PY_STRING_FROM_STRING("."));
+  PyList_Append(py_path, PyUnicode_FromString("."));
 
   // if LAMMPS_POTENTIALS environment variable is set, add it to PYTHONPATH as well
   const char *potentials_path = getenv("LAMMPS_POTENTIALS");
   if (potentials_path != nullptr) {
-    PyList_Append(py_path, PY_STRING_FROM_STRING(potentials_path));
+    PyList_Append(py_path, PyUnicode_FromString(potentials_path));
   }
   PyGILState_Release(gstate);
   if (coefffilename) read_coeffs(coefffilename);

src/PYTHON/fix_python_invoke.cpp

@@ -70,7 +70,7 @@ FixPythonInvoke::FixPythonInvoke(LAMMPS *lmp, int narg, char **arg) :
     error->all(FLERR,"Could not find Python function");
   }
 
-  lmpPtr = PY_VOID_POINTER(lmp);
+  lmpPtr = PyCapsule_New((void *)lmp, nullptr, nullptr);
 
   // nvalid = next step on which end_of_step or post_force does something
   // add nextvalid() to all computes that store invocation times

src/PYTHON/fix_python_move.cpp

@@ -44,7 +44,7 @@ FixPythonMove::FixPythonMove(LAMMPS *lmp, int narg, char **arg) :
 
   // add current directory to PYTHONPATH
   PyObject *py_path = PySys_GetObject((char *)"path");
-  PyList_Append(py_path, PY_STRING_FROM_STRING("."));
+  PyList_Append(py_path, PyUnicode_FromString("."));
 
 
   // create integrator instance
@@ -73,7 +73,7 @@ FixPythonMove::FixPythonMove(LAMMPS *lmp, int narg, char **arg) :
     error->all(FLERR,"Could not find integrator class {} in module {}", cls_name, module_name);
   }
 
-  PyObject *ptr = PY_VOID_POINTER(lmp);
+  PyObject *ptr = PyCapsule_New((void *)lmp, nullptr, nullptr);
   PyObject *py_move_obj = PyObject_CallFunction(py_move_type, (char *)"O", ptr);
   Py_CLEAR(ptr);
 

src/PYTHON/pair_python.cpp

@@ -54,14 +54,14 @@ PairPython::PairPython(LAMMPS *lmp) : Pair(lmp) {
 
   PyUtils::GIL lock;
   PyObject *py_path = PySys_GetObject((char *)"path");
-  PyList_Append(py_path, PY_STRING_FROM_STRING("."));
+  PyList_Append(py_path, PyUnicode_FromString("."));
 
   // if LAMMPS_POTENTIALS environment variable is set,
   // add it to PYTHONPATH as well
 
   const char *potentials_path = getenv("LAMMPS_POTENTIALS");
   if (potentials_path != nullptr) {
-    PyList_Append(py_path, PY_STRING_FROM_STRING(potentials_path));
+    PyList_Append(py_path, PyUnicode_FromString(potentials_path));
   }
 }
 

src/PYTHON/python_compat.h

@@ -16,22 +16,11 @@
 
 #include <Python.h>
 
-// Wrap API changes between Python 2 and 3 using macros
+#if PY_VERSION_HEX < 0x030600f0
-#if PY_MAJOR_VERSION == 2
+#error Python version 3.6 or later is required by LAMMPS
-#if defined(_MSC_VER) || defined(__MINGW32__)
-#define PY_INT_FROM_LONG(X) PyLong_FromLongLong(X)
-#define PY_INT_AS_LONG(X) PyLong_AsLongLong(X)
-#define PY_LONG_FROM_STRING(X) std::stoll(X)
-#else
-#define PY_INT_FROM_LONG(X) PyInt_FromLong(X)
-#define PY_INT_AS_LONG(X) PyInt_AsLong(X)
-#define PY_LONG_FROM_STRING(X) std::stol(X)
 #endif
-#define PY_STRING_FROM_STRING(X) PyString_FromString(X)
-#define PY_VOID_POINTER(X) PyCObject_FromVoidPtr((void *) X, nullptr)
-#define PY_STRING_AS_STRING(X) PyString_AsString(X)
 
-#elif PY_MAJOR_VERSION == 3
+// Wrap API differences between platforms using macros
 #if defined(_MSC_VER) || defined(__MINGW32__)
 #define PY_INT_FROM_LONG(X) PyLong_FromLongLong(X)
 #define PY_INT_AS_LONG(X) PyLong_AsLongLong(X)
@@ -41,9 +30,5 @@
 #define PY_INT_AS_LONG(X) PyLong_AsLong(X)
 #define PY_LONG_FROM_STRING(X) std::stol(X)
 #endif
-#define PY_STRING_FROM_STRING(X) PyUnicode_FromString(X)
-#define PY_VOID_POINTER(X) PyCapsule_New((void *) X, nullptr, nullptr)
-#define PY_STRING_AS_STRING(X) PyUnicode_AsUTF8(X)
-#endif
 
 #endif

src/PYTHON/python_impl.cpp

@@ -361,12 +361,12 @@ void PythonImpl::invoke_function(int ifunc, char *result)
         if (!str)
           error->all(FLERR, "Could not evaluate Python function {} input variable: {}",
                      pfuncs[ifunc].name, pfuncs[ifunc].svalue[i]);
-        pValue = PY_STRING_FROM_STRING(str);
+        pValue = PyUnicode_FromString(str);
       } else {
-        pValue = PY_STRING_FROM_STRING(pfuncs[ifunc].svalue[i]);
+        pValue = PyUnicode_FromString(pfuncs[ifunc].svalue[i]);
       }
     } else if (itype == PTR) {
-      pValue = PY_VOID_POINTER(lmp);
+      pValue = PyCapsule_New((void *)lmp, nullptr, nullptr);
     } else {
       error->all(FLERR, "Unsupported variable type: {}", itype);
     }
@@ -397,7 +397,7 @@ void PythonImpl::invoke_function(int ifunc, char *result)
       auto value = fmt::format("{:.15g}", PyFloat_AsDouble(pValue));
       strncpy(result, value.c_str(), Variable::VALUELENGTH - 1);
     } else if (otype == STRING) {
-      const char *pystr = PY_STRING_AS_STRING(pValue);
+      const char *pystr = PyUnicode_AsUTF8(pValue);
       if (pfuncs[ifunc].longstr)
         strncpy(pfuncs[ifunc].longstr, pystr, pfuncs[ifunc].length_longstr);
       else