gh-155742: Use PyBytesWriter in Python/assemble.c (#155747)

https://github.com/python/cpython/commit/09b63170e339cae3c10d2a3fe0f115b5305f8e3f
commit: 09b63170e339cae3c10d2a3fe0f115b5305f8e3f
branch: main
author: Victor Stinner <[email protected]>
committer: vstinner <[email protected]>
date: 2026-08-14T16:09:07Z
summary:

gh-155742: Use PyBytesWriter in Python/assemble.c (#155747)

Replace soft deprecated PyBytes_FromStringAndSize() with
PyBytesWriter.

files:
M Python/assemble.c

diff --git a/Python/assemble.c b/Python/assemble.c
index 8bcb4c7bf3a9aa..4bbebe30299906 100644
--- a/Python/assemble.c
+++ b/Python/assemble.c
@@ -54,7 +54,8 @@ struct assembler {
     int a_except_table_off;    /* offset into exception table */
     /* Location Info */
     int a_lineno;          /* lineno of last emitted instruction */
-    PyObject* a_linetable; /* bytes containing location info */
+    PyBytesWriter *a_linetable_writer; /* writer containing location info */
+    PyObject *a_linetable; /* bytes object containing location info */
     int a_location_off;    /* offset of last written location info frame */
 };
 
@@ -63,15 +64,12 @@ assemble_init(struct assembler *a, int firstlineno)
 {
     memset(a, 0, sizeof(struct assembler));
     a->a_lineno = firstlineno;
-    a->a_linetable = NULL;
-    a->a_location_off = 0;
-    a->a_except_table = NULL;
     a->a_bytecode = PyBytes_FromStringAndSize(NULL, DEFAULT_CODE_SIZE);
     if (a->a_bytecode == NULL) {
         goto error;
     }
-    a->a_linetable = PyBytes_FromStringAndSize(NULL, DEFAULT_CNOTAB_SIZE);
-    if (a->a_linetable == NULL) {
+    a->a_linetable_writer = PyBytesWriter_Create(DEFAULT_CNOTAB_SIZE);
+    if (a->a_linetable_writer == NULL) {
         goto error;
     }
     a->a_except_table = PyBytes_FromStringAndSize(NULL, DEFAULT_LNOTAB_SIZE);
@@ -81,7 +79,7 @@ assemble_init(struct assembler *a, int firstlineno)
     return SUCCESS;
 error:
     Py_CLEAR(a->a_bytecode);
-    Py_CLEAR(a->a_linetable);
+    PyBytesWriter_Discard(a->a_linetable_writer);
     Py_CLEAR(a->a_except_table);
     return ERROR;
 }
@@ -90,6 +88,7 @@ static void
 assemble_free(struct assembler *a)
 {
     Py_XDECREF(a->a_bytecode);
+    PyBytesWriter_Discard(a->a_linetable_writer);
     Py_XDECREF(a->a_linetable);
     Py_XDECREF(a->a_except_table);
 }
@@ -195,7 +194,8 @@ assemble_exception_table(struct assembler *a, instr_sequence *instrs)
 static void
 write_location_byte(struct assembler* a, int val)
 {
-    PyBytes_AS_STRING(a->a_linetable)[a->a_location_off] = val&255;
+    uint8_t *linetable = PyBytesWriter_GetData(a->a_linetable_writer);
+    linetable[a->a_location_off] = val & 255;
     a->a_location_off++;
 }
 
@@ -203,8 +203,8 @@ write_location_byte(struct assembler* a, int val)
 static uint8_t *
 location_pointer(struct assembler* a)
 {
-    return (uint8_t *)PyBytes_AS_STRING(a->a_linetable) +
-        a->a_location_off;
+    uint8_t *linetable = PyBytesWriter_GetData(a->a_linetable_writer);
+    return linetable + a->a_location_off;
 }
 
 static void
@@ -285,10 +285,10 @@ write_location_info_no_column(struct assembler* a, int length, int line_delta)
 static int
 write_location_info_entry(struct assembler* a, location loc, int isize)
 {
-    Py_ssize_t len = PyBytes_GET_SIZE(a->a_linetable);
+    Py_ssize_t len = PyBytesWriter_GetSize(a->a_linetable_writer);
     if (a->a_location_off + THEORETICAL_MAX_ENTRY_SIZE >= len) {
         assert(len > THEORETICAL_MAX_ENTRY_SIZE);
-        RETURN_IF_ERROR(_PyBytes_Resize(&a->a_linetable, len*2));
+        RETURN_IF_ERROR(PyBytesWriter_Resize(a->a_linetable_writer, len * 2));
     }
     if (loc.lineno == NO_LOCATION.lineno) {
         write_location_info_none(a, isize);
@@ -447,7 +447,12 @@ assemble_emit(struct assembler *a, instr_sequence *instrs,
     RETURN_IF_ERROR(_PyBytes_Resize(&a->a_except_table, a->a_except_table_off));
     RETURN_IF_ERROR(_PyCompile_ConstCacheMergeOne(const_cache, &a->a_except_table));
 
-    RETURN_IF_ERROR(_PyBytes_Resize(&a->a_linetable, a->a_location_off));
+    a->a_linetable = PyBytesWriter_FinishWithSize(a->a_linetable_writer,
+                                                  a->a_location_off);
+    a->a_linetable_writer = NULL;
+    if (a->a_linetable == NULL) {
+        return ERROR;
+    }
     RETURN_IF_ERROR(_PyCompile_ConstCacheMergeOne(const_cache, &a->a_linetable));
 
     RETURN_IF_ERROR(_PyBytes_Resize(&a->a_bytecode, a->a_offset * sizeof(_Py_CODEUNIT)));

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