Partially Use f string (#10218)

* flynt. trial 1.

* Trial 1.

* Addressed code review.

python/ray/memory_monitor.py

@@ -49,7 +49,7 @@ class RayOutOfMemoryError(Exception):
         return ("More than {}% of the memory on ".format(int(
             100 * threshold)) + "node {} is used ({} / {} GB). ".format(
                 platform.node(), round(used_gb, 2), round(total_gb, 2)) +
-                "The top 10 memory consumers are:\n\n{}".format(proc_str) +
+                f"The top 10 memory consumers are:\n\n{proc_str}" +
                 "\n\nIn addition, up to {} GiB of shared memory is ".format(
                     round(get_shared(psutil.virtual_memory()) / (1024**3), 2))
                 + "currently being used by the Ray object store. You can set "
@@ -134,8 +134,7 @@ class MemoryMonitor:
                     RayOutOfMemoryError.get_message(used_gb, total_gb,
                                                     self.error_threshold))
             else:
-                logger.debug("Memory usage is {} / {}".format(
-                    used_gb, total_gb))
+                logger.debug(f"Memory usage is {used_gb} / {total_gb}")
 
             if self.heap_limit:
                 mem_info = psutil.Process(os.getpid()).memory_info()