Create mule_fields_subset.py

This is the beginnings of a few ideas I had to change um_fields_subset. that I explored while trying to figure out a way to remove the timeseries

Author: leoberhelman

src/mule_fields_subset.py

@@ -0,0 +1,32 @@
+import mule
+import numpy as np
+
+def remove_fields(umfile, output_file, fields_to_remove):
+    """
+    This function so far does all of the work 
+    """ 
+    # Iterate over a copy of `um_file.fields` to avoid modifying the list while looping
+    for field in um_file.fields[:]:
+    
+        if field.lbuser4 in fields_to_remove:
+        #if field.stash in fields_to_remove:
+    
+            um_file.fields.remove(field)  # Directly remove the field if it matches
+
+    # Save the modified UM file
+    um_file.to_file(output_file)
+
+def main()
+
+    # Define input/output file paths and the fields you want to remove
+    input_file = "/home/198/lo9311/access-esm1.5/preindustrial+concentrations/archive/restart000/atmosphere/restart_dump_old_perturb.astart"
+    output_file = "/home/198/lo9311/access-esm1.5/preindustrial+concentrations/archive/restart000/atmosphere/modified_file.astart"
+    fields_to_remove = [155,156,3100, 3101, 33001, 33002]  # Example list of STASH codes or section numbers to remove
+
+    um_file = mule.UMfile.from_file(input_file)
+    
+
+    remove_fields(um_file, output_file, fields_to_remove)
+
+if __name == "__main__":
+    main()