Require files to be an iterator, not a list

Preparing for a check on the first file.

Inst_eddies/inst_eddies.py.in

@@ -45,10 +45,10 @@ def process_1_file(bbox, nco_instance, nc_file, cropped_fname, unpacked_fname,
 
 
 def loop_inst_eddies(files, bbox, d, my_slice):
-    """files is a sequence or iterator of file paths. The first file must
-    exist, others can be missing. bbox is a tuple of four real
-    numbers. d is a date index (integer value) for the first
-    date. my_slice is the slice index (integer value) in the SHPC.
+    """files is an iterator of file paths. The first file must exist,
+    others can be missing. bbox is a tuple of four real numbers. d is
+    a date index (integer value) for the first date. my_slice is the
+    slice index (integer value) in the SHPC.
 
     """
 
@@ -130,4 +130,4 @@ if __name__ == "__main__":
     d = int(d)
     my_slice = input("Enter slice index (integer value): ")
     my_slice = int(my_slice)
-    loop_inst_eddies(args.file, args.bbox, d, my_slice)
+    loop_inst_eddies(iter(args.file), args.bbox, d, my_slice)