Use cupy when available with the particle container wrapper

Python/pywarpx/LoadThirdParty.py

@@ -0,0 +1,35 @@
+# This file is part of WarpX.
+#
+# Authors: Axel Huebl
+# License: BSD-3-Clause-LBNL
+
+from ._libwarpx import libwarpx
+
+
+def load_cupy():
+    """
+    This is a helper for
+    https://docs.cupy.dev/en/stable/user_guide/basic.html
+    """
+    amr = libwarpx.amr
+    status = None
+
+    if amr.Config.have_gpu:
+        try:
+            import cupy as cp
+            xp = cp
+            # Note: found and will use cupy
+        except ImportError:
+            status = "Warning: GPU found but cupy not available! Trying managed memory in numpy..."
+            import numpy as np
+            xp = np
+        if amr.Config.gpu_backend == "SYCL":
+            status = "Warning: SYCL GPU backend not yet implemented for Python"
+            import numpy as np
+            xp = np
+
+    else:
+        import numpy as np
+        xp = np
+        # Note: found and will use numpy
+    return xp, status

Python/pywarpx/__init__.py

@@ -34,6 +34,7 @@
 from .HybridPICModel import hybridpicmodel
 from .Interpolation import interpolation
 from .Lasers import lasers
+from .LoadThirdParty import load_cupy
 from .PSATD import psatd
 from .Particles import newspecies, particles
 from .WarpX import warpx