python
@@ -426,6 +426,7 @@ def _write_atomic(path, data, mode=0o666):
 #     Python 3.12a1 3510 (FOR_ITER leaves iterator on the stack)
 #     Python 3.12a1 3511 (Add STOPITERATION_ERROR instruction)
 #     Python 3.12a1 3512 (Remove all unused consts from code objects)
+#     Python 3.12a1 3513 (Compress marshalled bytecode)
 
 #     Python 3.13 will start with 3550
 
@@ -438,7 +439,7 @@ def _write_atomic(path, data, mode=0o666):
 # Whenever MAGIC_NUMBER is changed, the ranges in the magic_values array
 # in PC/launcher.c must also be updated.
 
-MAGIC_NUMBER = (3512).to_bytes(2, 'little') + b'\r\n'
+MAGIC_NUMBER = (3513).to_bytes(2, 'little') + b'\r\n'
 
 _RAW_MAGIC_NUMBER = int.from_bytes(MAGIC_NUMBER, 'little')  # For import.c
 

diff --git a/Lib/opcode.py b/Lib/opcode.py
@@ -205,7 +205,7 @@ def pseudo_op(name, op, real_ops):
 hasfree.append(148)
 def_op('COPY_FREE_VARS', 149)
 def_op('YIELD_VALUE', 150)
-def_op('RESUME', 151)   # This must be kept in sync with deepfreeze.py
+def_op('RESUME', 151)
 def_op('MATCH_CLASS', 152)
 
 def_op('FORMAT_VALUE', 155)

diff --git a/Misc/NEWS.d/next/Library/2022-11-16-05-37-32.gh-issue-99554.4sJH79.rst b/Misc/NEWS.d/next/Library/2022-11-16-05-37-32.gh-issue-99554.4sJH79.rst
@@ -0,0 +1 @@
+Modify the :mod:`marshal` format to serialize bytecode more efficiently.
diff --git a/Python/marshal.c b/Python/marshal.c
@@ -12,6 +12,7 @@
 #include "pycore_call.h"          // _PyObject_CallNoArgs()
 #include "pycore_code.h"          // _PyCode_New()
 #include "pycore_hashtable.h"     // _Py_hashtable_t
+#include "pycore_opcode.h"
 #include "marshal.h"              // Py_MARSHAL_VERSION
 
 /*[clinic input]
@@ -291,6 +292,26 @@ w_float_str(double v, WFILE *p)
     PyMem_Free(buf);
 }
 
+static void 
+w_bytecode(PyCodeObject *code, WFILE *p)
+{
+    W_SIZE(Py_SIZE(code), p);
+    for (Py_ssize_t i = 0; i < Py_SIZE(code); i++) {
+        _Py_CODEUNIT instruction = _PyCode_CODE(code)[i];
+        int opcode = _PyOpcode_Deopt[_Py_OPCODE(instruction)];
+        w_byte(opcode, p);
+        if (HAS_ARG(opcode)) {
+            w_byte(_Py_OPARG(instruction), p);
+        }
+        i += _PyOpcode_Caches[opcode];
+    }
+    // Terminate with two zero bytes, so that programs scanning .pyc files can
+    // skip over the bytecode (even if they don't know the compression scheme).
+    // This is simpler than writing the compressed size in the header, which
+    // requires two loops (one to count the bytes, then one to write them):
+    w_short(0, p);
+}
+
 static int
 w_ref(PyObject *v, char *flag, WFILE *p)
 {
@@ -550,18 +571,13 @@ w_complex_object(PyObject *v, char flag, WFILE *p)
     }
     else if (PyCode_Check(v)) {
         PyCodeObject *co = (PyCodeObject *)v;
-        PyObject *co_code = _PyCode_GetCode(co);
-        if (co_code == NULL) {
-            p->error = WFERR_NOMEMORY;
-            return;
-        }
         W_TYPE(TYPE_CODE, p);
         w_long(co->co_argcount, p);
         w_long(co->co_posonlyargcount, p);
         w_long(co->co_kwonlyargcount, p);
         w_long(co->co_stacksize, p);
         w_long(co->co_flags, p);
-        w_object(co_code, p);
+        w_bytecode(co, p);
         w_object(co->co_consts, p);
         w_object(co->co_names, p);
         w_object(co->co_localsplusnames, p);
@@ -572,7 +588,6 @@ w_complex_object(PyObject *v, char flag, WFILE *p)
         w_long(co->co_firstlineno, p);
         w_object(co->co_linetable, p);
         w_object(co->co_exceptiontable, p);
-        Py_DECREF(co_code);
     }
     else if (PyObject_CheckBuffer(v)) {
         /* Write unknown bytes-like objects as a bytes object */
@@ -921,6 +936,67 @@ r_float_str(RFILE *p)
     return PyOS_string_to_double(buf, NULL, NULL);
 }
 
+static PyObject *
+r_bytecode(RFILE *p)
+{
+    long size = r_long(p);
+    if (PyErr_Occurred()) {
+        return NULL;
+    }
+    Py_ssize_t nbytes = size * sizeof(_Py_CODEUNIT);
+    if (nbytes < 0 || SIZE32_MAX < nbytes) {
+        const char *e = "bad marshal data (bytecode size out of range)";
+        PyErr_SetString(PyExc_ValueError, e);
+        return NULL;
+    }
+    PyObject *bytecode = PyBytes_FromStringAndSize(NULL, nbytes);
+    if (bytecode == NULL) {
+        return NULL;
+    }
+    _Py_CODEUNIT *buffer = (_Py_CODEUNIT *)PyBytes_AS_STRING(bytecode);
+    long i = 0;
+    while (i < size) {
+        int opcode = r_byte(p);
+        if (opcode == EOF) {
+            const char *e = "EOF read where opcode expected";
+            PyErr_SetString(PyExc_EOFError, e);
+            return NULL;
+        }
+        int oparg;
+        if (HAS_ARG(opcode)) {
+            oparg = r_byte(p);
+            if (oparg == EOF) {
+                const char *e = "EOF read where oparg expected";
+                PyErr_SetString(PyExc_EOFError, e);
+                return NULL;
+            }
+        }
+        else {
+            oparg = 0;
+        }
+        assert(0x01 <= opcode && opcode <= 0xFF);
+        assert(0x00 <= oparg && oparg <= 0xFF);
+        buffer[i].opcode = opcode;
+        buffer[i].oparg = oparg;
+        i++;
+        for (int j = 0; j < _PyOpcode_Caches[opcode]; j++) {
+            assert(i < size);
+            buffer[i].opcode = CACHE;
+            buffer[i].oparg = 0;
+            i++;
+        }
+    }
+    // The compressed bytecode is terminated with two zero bytes (see the
+    // comment at the bottom of w_bytecode):
+    int zero_zero = r_short(p);
+    if (zero_zero == EOF || zero_zero != 0 || i != size) {
+        const char *e = "bad marshal data (bytecode size incorrect)";
+        PyErr_SetString(PyExc_ValueError, e);
+        return NULL;
+    }
+    return bytecode;
+}
+
 /* allocate the reflist index for a new object. Return -1 on failure */
 static Py_ssize_t
 r_ref_reserve(int flag, RFILE *p)
@@ -1378,7 +1454,7 @@ r_object(RFILE *p)
             flags = (int)r_long(p);
             if (PyErr_Occurred())
                 goto code_error;
-            code = r_object(p);
+            code = r_bytecode(p);
             if (code == NULL)
                 goto code_error;
             consts = r_object(p);

@@ -17,13 +17,15 @@
 from typing import Dict, FrozenSet, TextIO, Tuple
 
 import umarshal
+import opcode_for_build
 from generate_global_objects import get_identifiers_and_strings
 
+opcode = opcode_for_build.import_opcode()
+
 verbose = False
 identifiers, strings = get_identifiers_and_strings()
 
-# This must be kept in sync with opcode.py
-RESUME = 151
+RESUME = opcode.opmap["RESUME"]
 
 def isprintable(b: bytes) -> bool:
     return all(0x20 <= c < 0x7f for c in b)

diff --git a/Tools/build/opcode_for_build.py b/Tools/build/opcode_for_build.py
@@ -0,0 +1,27 @@
+"""
+Parts of our build process (looking at you, deepfreeze) need the opcode module
+for the Python *being built*, not the Python *doing the building*.
+
+This basically just loads ../../Lib/opcode.py:
+
+>>> import opcode_for_build
+>>> opcode = opcode_for_build.import_opcode()
+"""
+
+import os
+import types
+
+_OPCODE_PATH = os.path.realpath(
+    os.path.join(
+        os.path.dirname(__file__), os.pardir, os.pardir, "Lib", "opcode.py"
+    )
+)
+
+def import_opcode() -> types.ModuleType:
+    """Import the current version of the opcode module (from Lib)."""
+    opcode_module = types.ModuleType("opcode")
+    opcode_module.__file__ = os.path.realpath(_OPCODE_PATH)
+    with open(_OPCODE_PATH, encoding="utf-8") as opcode_file:
+        # Don't try this at home, kids:
+        exec(opcode_file.read(), opcode_module.__dict__)
+    return opcode_module
diff --git a/Tools/build/umarshal.py b/Tools/build/umarshal.py
@@ -1,9 +1,12 @@
 # Implementat marshal.loads() in pure Python
 
 import ast
+import opcode_for_build
 
 from typing import Any, Tuple
 
+opcode = opcode_for_build.import_opcode()
+
 
 class Type:
     # Adapted from marshal.c
@@ -47,6 +50,8 @@ class Type:
 CO_FAST_CELL = 0x40
 CO_FAST_FREE = 0x80
 
+CACHE = opcode.opmap["CACHE"]
+
 
 class Code:
     def __init__(self, **kwds: Any):
@@ -178,6 +183,24 @@ def r_object(self) -> Any:
         finally:
             self.level = old_level
 
+    def r_bytecode(self) -> bytes:
+        nbytes = self.r_long() * 2
+        bytecode = bytearray()
+        while len(bytecode) < nbytes:
+            opcode_byte = self.r_byte()
+            if opcode_byte >= opcode.HAVE_ARGUMENT:
+                oparg_byte = self.r_byte()
+            else:
+                oparg_byte = 0
+            assert 0x01 <= opcode_byte <= 0xFF
+            assert 0x00 <= oparg_byte <= 0xFF
+            bytecode.extend([opcode_byte, oparg_byte])
+            for _ in range(opcode._inline_cache_entries[opcode_byte]):
+                bytecode.extend([CACHE, 0])
+        zero_zero = self.r_short()
+        assert zero_zero == 0 and len(bytecode) == nbytes
+        return bytes(bytecode)
+
     def _r_object(self) -> Any:
         code = self.r_byte()
         flag = code & FLAG_REF
@@ -279,7 +302,7 @@ def R_REF(obj: Any) -> Any:
             retval.co_kwonlyargcount = self.r_long()
             retval.co_stacksize = self.r_long()
             retval.co_flags = self.r_long()
-            retval.co_code = self.r_object()
+            retval.co_code = self.r_bytecode()
             retval.co_consts = self.r_object()
             retval.co_names = self.r_object()
             retval.co_localsplusnames = self.r_object()
Original file line number	Diff line number	Diff line change
		@@ -0,0 +1 @@
		Modify the :mod:`marshal` format to serialize bytecode more efficiently.