Implement fallback case

lbmpy/max_domain_size_info.py

@@ -41,6 +41,15 @@ except ImportError:
     cupy = None
     device = None
 
+if cupy:
+    try:
+        device = cupy.cuda.Device(pystencils.GPU_DEVICE)
+    except AttributeError:
+        warnings.warn("You are using an old pystencils version. Consider updating it")
+        device = cupy.cuda.Device(0)
+else:
+    device = None
+
 try:
     from psutil import virtual_memory
 except ImportError: