Move _RAW_MAGIC_NUMBER to the C side as well

Author: mdboom

Include/internal/pycore_magic_number.h

@@ -268,6 +268,8 @@ PC/launcher.c must also be updated.
 */
 
 #define PYC_MAGIC_NUMBER 3603
+#define PYC_MAGIC_NUMBER_TOKEN ((uint32_t)PYC_MAGIC_NUMBER | ((uint32_t)'\r' << 16) | ((uint32_t)'\n' << 24))
+
 
 #ifdef __cplusplus
 }

Lib/importlib/_bootstrap_external.py

@@ -223,8 +223,6 @@ def _write_atomic(path, data, mode=0o666):
 
 MAGIC_NUMBER = (_imp._pyc_magic_number).to_bytes(2, 'little') + b'\r\n'
 
-_RAW_MAGIC_NUMBER = int.from_bytes(MAGIC_NUMBER, 'little')  # for import.c
-
 _PYCACHE = '__pycache__'
 _OPT = 'opt-'
 
@@ -862,7 +860,7 @@ def get_code(self, fullname):
                                  _imp.check_hash_based_pycs == 'always')):
                                 source_bytes = self.get_data(source_path)
                                 source_hash = _imp.source_hash(
-                                    _RAW_MAGIC_NUMBER,
+                                    _imp._pyc_magic_number_token,
                                     source_bytes,
                                 )
                                 _validate_hash_pyc(data, source_hash, fullname,
@@ -891,7 +889,7 @@ def get_code(self, fullname):
                 source_mtime is not None):
             if hash_based:
                 if source_hash is None:
-                    source_hash = _imp.source_hash(_RAW_MAGIC_NUMBER,
+                    source_hash = _imp.source_hash(_imp._pyc_magic_number_token,
                                                    source_bytes)
                 data = _code_to_hash_pyc(code_object, source_hash, check_source)
             else:

Lib/importlib/util.py

@@ -5,7 +5,6 @@
 from ._bootstrap import spec_from_loader
 from ._bootstrap import _find_spec
 from ._bootstrap_external import MAGIC_NUMBER
-from ._bootstrap_external import _RAW_MAGIC_NUMBER
 from ._bootstrap_external import cache_from_source
 from ._bootstrap_external import decode_source
 from ._bootstrap_external import source_from_cache
@@ -18,7 +17,7 @@
 
 def source_hash(source_bytes):
     "Return the hash of *source_bytes* as used in hash-based pyc files."
-    return _imp.source_hash(_RAW_MAGIC_NUMBER, source_bytes)
+    return _imp.source_hash(_imp._pyc_magic_number_token, source_bytes)
 
 
 def resolve_name(name, package):

Lib/test/test_import/__init__.py

@@ -3113,6 +3113,15 @@ def test_pyimport_addmodule_create(self):
         self.assertIs(mod, sys.modules[name])
 
 
+@cpython_only
+class TestMagicNumber(unittest.TestCase):
+    def test_magic_number_endianness(self):
+        magic_number = (_imp._pyc_magic_number).to_bytes(2, 'little') + b'\r\n'
+        raw_magic_number = int.from_bytes(magic_number, 'little')
+
+        assert raw_magic_number == _imp._pyc_magic_number_token
+
+
 if __name__ == '__main__':
     # Test needs to be a package, so we can do relative imports.
     unittest.main()

Lib/zipimport.py

@@ -705,7 +705,7 @@ def _unmarshal_code(self, pathname, fullpath, fullname, data):
             source_bytes = _get_pyc_source(self, fullpath)
             if source_bytes is not None:
                 source_hash = _imp.source_hash(
-                    _bootstrap_external._RAW_MAGIC_NUMBER,
+                    _imp._pyc_magic_number_token,
                     source_bytes,
                 )
 

Python/import.c

@@ -2477,22 +2477,7 @@ _PyImport_GetBuiltinModuleNames(void)
 long
 PyImport_GetMagicNumber(void)
 {
-    union magic_number {
-        uint32_t raw;
-        uint8_t parts[4];
-    } n;
-
-    n.parts[0] = (uint16_t)PYC_MAGIC_NUMBER & 0xff;
-    n.parts[1] = (uint16_t)PYC_MAGIC_NUMBER >> 8;
-    n.parts[2] = '\r';
-    n.parts[3] = '\n';
-
-#if PY_BIG_ENDIAN
-    uint32_t result = _Py_bswap32(n.raw);
-    return (long)result;
-#else
-    return (long)n.raw;
-#endif
+    return PYC_MAGIC_NUMBER_TOKEN;
 }
 
 extern const char * _PySys_ImplCacheTag;
@@ -4830,6 +4815,10 @@ imp_module_exec(PyObject *module)
         return -1;
     }
 
+    if (PyModule_AddIntConstant(module, "_pyc_magic_number_token", PYC_MAGIC_NUMBER_TOKEN) < 0) {
+        return -1;
+    }
+
     return 0;
 }