code: def optimize(p):
      "Optimize a pickle string by removing unused PUT opcodes"
      put = "PUT"
      get = "GET"
      oldids = set()  # set of all PUT ids
      newids = {}  # set of ids used by a GET opcode
      opcodes = []  # (op, idx) or (pos, end_pos)
      proto = 0
      protoheader = b""
      for opcode, arg, pos, end_pos in _genops(p, yield_end_pos=True):
          if "PUT" in opcode.name:
              oldids.add(arg)
              opcodes.append((put, arg))
          elif opcode.name == "MEMOIZE":
              idx = len(oldids)
              oldids.add(idx)
              opcodes.append((put, idx))
          elif "FRAME" in opcode.name:
              pass
          elif "GET" in opcode.name:
              if opcode.proto > proto:
                  proto = opcode.proto
              newids[arg] = None
              opcodes.append((get, arg))
          elif opcode.name == "PROTO":
              if arg > proto:
                  proto = arg
              if pos == 0:
                  protoheader = p[pos:end_pos]
              else:
                  opcodes.append((pos, end_pos))
          else:
              opcodes.append((pos, end_pos))
      del oldids
  
      # Copy the opcodes except for PUTS without a corresponding GET
      out = io.BytesIO()
      # Write the PROTO header before any framing
      out.write(protoheader)
      pickler = pickle._Pickler(out, proto)
      if proto >= 4:
          pickler.framer.start_framing()
      idx = 0
      for op, arg in opcodes:
          frameless = False
          if op is put:
              if arg not in newids:
                  continue
              data = pickler.put(idx)
              newids[arg] = idx
              idx += 1
          elif op is get:
              data = pickler.get(newids[arg])
          else:
              data = p[op:arg]
              frameless = len(data) > pickler.framer._FRAME_SIZE_TARGET
          pickler.framer.commit_frame(force=frameless)
          if frameless:
              pickler.framer.file_write(data)
          else:
              pickler.write(data)
      pickler.framer.end_framing()
      return out.getvalue()
  
imports: import codecs
  import io
  import pickle
  import re
  import sys
  from struct import unpack
  from pickle import decode_long
label_desc: Use image node_id 28 for calling a global function with example usage: optimize(p) and returns: out