Force setup_run_directory function to raise AttributeError if it does…

…n't have access to a cpu layout rather than throw generic error

regional_mom6/regional_mom6.py

@@ -437,6 +437,7 @@ def __init__(
         self.grid_type = grid_type
         self.repeat_year_forcing = repeat_year_forcing
         self.ocean_mask = None
+        self.layout = None # This should be a tuple. Leaving in a dummy 'None' makes it easy to remind the user to provide a value later on.
         if read_existing_grids:
             try:
                 self.hgrid = xr.open_dataset(self.mom_input_dir / "hgrid.nc")
@@ -1502,18 +1503,26 @@ def setup_run_directory(
             mask_table = p.name
             x, y = (int(v) for v in layout.split("x"))
             ncpus = (x * y) - int(masked)
+            layout = (x, y) # This is a local variable keeping track of the layout as read from the mask table. Not to be confused with self.layout which is unchanged and may differ. 
+
+            print(f"Mask table {p.name} read. Using this to infer the cpu layout {layout}, total masked out cells {masked}, and total number of CPUs {ncpus}.")
+
+
         if mask_table == None:
+            if self.layout == None:
+                raise AttributeError("No mask table found, and the cpu layout has not been set. At least one of these is requiret to set up the experiment.")
             print(
-                "No mask table found! This suggests the domain is mostly water, so there are "
+                f"No mask table found, but the cpu layout has been set to {self.layout} This suggests the domain is mostly water, so there are "
                 + "no `non compute` cells that are entirely land. If this doesn't seem right, "
-                + "ensure you've already run `FRE_tools`."
+                + "ensure you've already run the `FRE_tools` method which sets up the cpu mask table. Keep an eye on any errors that might print while"
+                + "the FRE tools (which run C++ in the background) are running."
             )
-            if not hasattr(self, "layout"):
-                raise AttributeError(
-                    "No layout information found. This suggests that `FRE_tools()` hasn't been called yet. "
-                    + "Please do so, in order for the number of processors required is computed."
-                )
-            ncpus = self.layout[0] * self.layout[1]
+            # Here we define a local copy of the layout just for use within this function. 
+            # This prevents the layout from being overwritten in the main class in case 
+            # in case the user accidentally loads in the wrong mask table.
+            layout = self.layout 
+            ncpus = layout[0] * layout[1]
+
         print("Number of CPUs required: ", ncpus)
 
         ## Modify the input namelists to give the correct layouts
@@ -1527,7 +1536,7 @@ def setup_run_directory(
                     else:
                         lines[jj] = "# MASKTABLE = no mask table"
                 if "LAYOUT =" in lines[jj] and "IO" not in lines[jj]:
-                    lines[jj] = f"LAYOUT = {self.layout[1]},{self.layout[0]}\n"
+                    lines[jj] = f"LAYOUT = {layout[1]},{layout[0]}\n"
 
                 if "NIGLOBAL" in lines[jj]:
                     lines[jj] = f"NIGLOBAL = {self.hgrid.nx.shape[0]//2}\n"