Issue #18192: Introduce importlib.util.MAGIC_NUMBER and document the

deprecation of imp.get_magic().

4 files changed, 22 insertions, 6 deletions

diff --git a/Lib/imp.py b/Lib/imp.py
index ad0fd6a..e06fbe6 100644
--- a/Lib/imp.py
+++ b/Lib/imp.py
@@ -23,6 +23,7 @@ from importlib._bootstrap import cache_from_source, source_from_cache
 
 from importlib import _bootstrap
 from importlib import machinery
+from importlib import util
 import importlib
 import os
 import sys
@@ -44,8 +45,11 @@ IMP_HOOK = 9
 
 
 def get_magic():
-    """Return the magic number for .pyc or .pyo files."""
-    return _bootstrap._MAGIC_BYTES
+    """**DEPRECATED**
+
+    Return the magic number for .pyc or .pyo files.
+    """
+    return util.MAGIC_NUMBER
 
 
 def get_tag():
diff --git a/Lib/importlib/_bootstrap.py b/Lib/importlib/_bootstrap.py
index 9a82bd1..4558054 100644
--- a/Lib/importlib/_bootstrap.py
+++ b/Lib/importlib/_bootstrap.py
@@ -383,8 +383,8 @@ def _call_with_frames_removed(f, *args, **kwds):
 # longer be understood by older implementations of the eval loop (usually
 # due to the addition of new opcodes).
 
-_MAGIC_BYTES = (3280).to_bytes(2, 'little') + b'\r\n'
-_RAW_MAGIC_NUMBER = int.from_bytes(_MAGIC_BYTES, 'little')  # For import.c
+MAGIC_NUMBER = (3280).to_bytes(2, 'little') + b'\r\n'
+_RAW_MAGIC_NUMBER = int.from_bytes(MAGIC_NUMBER, 'little')  # For import.c
 
 _PYCACHE = '__pycache__'
 
@@ -663,7 +663,7 @@ def _validate_bytecode_header(data, source_stats=None, name=None, path=None):
     magic = data[:4]
     raw_timestamp = data[4:8]
     raw_size = data[8:12]
-    if magic != _MAGIC_BYTES:
+    if magic != MAGIC_NUMBER:
         message = 'bad magic number in {!r}: {!r}'.format(name, magic)
         _verbose_message(message)
         raise ImportError(message, **exc_details)
@@ -711,7 +711,7 @@ def _compile_bytecode(data, name=None, bytecode_path=None, source_path=None):
 def _code_to_bytecode(code, mtime=0, source_size=0):
     """Compile a code object into bytecode for writing out to a byte-compiled
     file."""
-    data = bytearray(_MAGIC_BYTES)
+    data = bytearray(MAGIC_NUMBER)
     data.extend(_w_long(mtime))
     data.extend(_w_long(source_size))
     data.extend(marshal.dumps(code))
diff --git a/Lib/importlib/util.py b/Lib/importlib/util.py
index 9cf0eb7..09ec03c 100644
--- a/Lib/importlib/util.py
+++ b/Lib/importlib/util.py
@@ -1,5 +1,6 @@
 """Utility code for constructing importers, etc."""
 
+from ._bootstrap import MAGIC_NUMBER
 from ._bootstrap import module_to_load
 from ._bootstrap import set_loader
 from ._bootstrap import set_package
diff --git a/Lib/test/test_importlib/test_util.py b/Lib/test/test_importlib/test_util.py
index e6b0084..78f5a3e 100644
--- a/Lib/test/test_importlib/test_util.py
+++ b/Lib/test/test_importlib/test_util.py
@@ -313,5 +313,16 @@ class ResolveNameTests(unittest.TestCase):
             util.resolve_name('..bacon', 'spam')
 
 
+class MagicNumberTests(unittest.TestCase):
+
+    def test_length(self):
+        # Should be 4 bytes.
+        self.assertEqual(len(util.MAGIC_NUMBER), 4)
+
+    def test_incorporates_rn(self):
+        # The magic number uses \r\n to come out wrong when splitting on lines.
+        self.assertTrue(util.MAGIC_NUMBER.endswith(b'\r\n'))
+
+
 if __name__ == '__main__':
     unittest.main()