fix interpolation

sergio.py

@@ -269,7 +269,7 @@ def main_get(args, pira: Pira):
     try:
         out = pira.read_variable(args.variable)
     except UnknownCommandError:
-        print("Variable not found: {args.variable}", file=sys.stderr)
+        print(f"Variable not found: {args.variable}", file=sys.stderr)
         sys.exit(1)
     output(args, dict(variable=args.variable, value=out))
 
@@ -278,7 +278,7 @@ def main_set(args, pira: Pira):
     try:
         pira.set_variable(args.variable, args.value, save=args.save)
     except UnknownCommandError:
-        print("Variable not found: {args.variable}", file=sys.stderr)
+        print(f"Variable not found: {args.variable}", file=sys.stderr)
         sys.exit(1)
 
 
@@ -286,7 +286,7 @@ def main_save(args, pira: Pira):
     try:
         pira.save_variable(args.variable)
     except UnknownCommandError:
-        print("Variable not found: {args.variable}", file=sys.stderr)
+        print(f"Variable not found: {args.variable}", file=sys.stderr)
         sys.exit(1)