use memoryview to avoid copying

Author: benjaminp

Lib/importlib/_bootstrap_external.py

@@ -797,7 +797,7 @@ def get_code(self, fullname):
                     }
                     try:
                         flags = _classify_pyc(data, fullname, exc_details)
-                        bytes_data = data[16:]
+                        bytes_data = memoryview(data)[16:]
                         hash_based = flags & 0b1 != 0
                         if hash_based:
                             check_source = flags & 0b10 != 0
@@ -943,7 +943,11 @@ def get_code(self, fullname):
             'path': path,
         }
         _classify_pyc(data, fullname, exc_details)
-        return _compile_bytecode(data[16:], name=fullname, bytecode_path=path)
+        return _compile_bytecode(
+            memoryview(data)[16:],
+            name=fullname,
+            bytecode_path=path,
+        )
 
     def get_source(self, fullname):
         """Return None as there is no source code."""

Lib/modulefinder.py

@@ -292,7 +292,7 @@ def load_module(self, fqname, fp, pathname, file_info):
             except ImportError as exc:
                 self.msgout(2, "raise ImportError: " + str(exc), pathname)
                 raise
-            co = marshal.loads(data[16:])
+            co = marshal.loads(memoryview(data)[16:])
         else:
             co = None
         m = self.add_module(fqname)