Issue #20791: copy.copy() now doesn't make a copy when the input is a bytes object. Initial patch by Peter Otten.

Lib/copy.py

@@ -110,7 +110,7 @@ _copy_dispatch = d = {}
 def _copy_immutable(x):
     return x
 for t in (type(None), int, float, bool, str, tuple,
-          frozenset, type, range,
+          bytes, frozenset, type, range,
           types.BuiltinFunctionType, type(Ellipsis),
           types.FunctionType, weakref.ref):
     d[t] = _copy_immutable

Lib/test/test_copy.py

@@ -98,6 +98,7 @@ class TestCopy(unittest.TestCase):
             pass
         tests = [None, 42, 2**100, 3.14, True, False, 1j,
                  "hello", "hello\u1234", f.__code__,
+                 b"world", bytes(range(256)),
                  NewStyle, range(10), Classic, max, WithMetaclass]
         for x in tests:
             self.assertIs(copy.copy(x), x)

Misc/NEWS

@@ -14,6 +14,9 @@ Core and Builtins
 Library
 -------
 
+- Issue #20791: copy.copy() now doesn't make a copy when the input is
+  a bytes object.  Initial patch by Peter Otten.
+
 - Issue #19748: On AIX, time.mktime() now raises an OverflowError for year
   outsize range [1902; 2037].