code: def set_should_persist(line):
      # this marker indicates that the logline should be persisted by
      # the receiver
      line = to_bytes(line)
      if is_structured(line) and not line.startswith(b"[!["):
          return b"[!" + line
      else:
          return line
  
file_path: metaflow/metaflow/mflog/mflog.py
imports: import heapq
  import re
  import time
  import uuid
  from datetime import datetime
  from collections import namedtuple
  from metaflow.util import to_bytes, to_fileobj, to_unicode
label_desc: Use image node_id 4 for calling a global function with example usage: set_should_persist(line) and returns: unknown, line