Simplifying and enhancing const_key

bytecode/instr.py

@@ -1,9 +1,8 @@
 import enum
 import dis
-import math
 import opcode as _opcode
 import sys
-import types
+from marshal import dumps as _dumps
 
 import bytecode as _bytecode
 
@@ -27,56 +26,12 @@ class Compare(enum.IntEnum):
 
 
 def const_key(obj):
-    # Python implmentation of the C function _PyCode_ConstantKey()
-    # of Python 3.6
-
-    obj_type = type(obj)
-    # Note: check obj_type == test_type rather than isinstance(obj, test_type)
-    # to not merge instance of subtypes
-
-    if (obj is None
-        or obj is Ellipsis
-            or obj_type in {int, bool, bytes, str, types.CodeType}):
-        return (obj_type, obj)
-
-    if obj_type == float:
-        # all we need is to make the tuple different in either the 0.0
-        # or -0.0 case from all others, just to avoid the "coercion".
-        if obj == 0.0 and math.copysign(1.0, obj) < 0:
-            return (obj_type, obj, None)
-        else:
-            return (obj_type, obj)
-
-    if obj_type == complex:
-        # For the complex case we must make complex(x, 0.)
-        # different from complex(x, -0.) and complex(0., y)
-        # different from complex(-0., y), for any x and y.
-        # All four complex zeros must be distinguished.
-        real_negzero = (obj.real == 0.0 and math.copysign(1.0, obj.real) < 0.0)
-        imag_negzero = (obj.imag == 0.0 and math.copysign(1.0, obj.imag) < 0.0)
-
-        # use True, False and None singleton as tags for the real and imag
-        # sign, to make tuples different
-        if real_negzero and imag_negzero:
-            return (obj_type, obj, True)
-        elif imag_negzero:
-            return (obj_type, obj, False)
-        elif real_negzero:
-            return (obj_type, obj, None)
-        else:
-            return (obj_type, obj)
-
-    if type(obj) == tuple:
-        key = tuple(const_key(item) for item in obj)
-        return (obj_type, obj, key)
-
-    if type(obj) == frozenset:
-        key = frozenset(const_key(item) for item in obj)
-        return (obj_type, obj, key)
-
-    # For other types, we use the object identifier as an unique identifier
-    # to ensure that they are seen as unequal.
-    return (obj_type, id(obj))
+    try:
+        return _dumps(obj)
+    except ValueError:
+        # For other types, we use the object identifier as an unique identifier
+        # to ensure that they are seen as unequal.
+        return (type(obj), id(obj))
 
 
 def _check_lineno(lineno):

bytecode/tests/test_instr.py

@@ -234,6 +234,35 @@ def check(instr):
         for arg in 2**31, 2**32, 2**63, 2**64, -1:
             self.assertEqual(Instr('LOAD_CONST', arg).stack_effect(), 1)
 
+    def test_code_object_containing_mutable_data(self):
+        from bytecode import Bytecode, Instr
+        from types import CodeType
+
+        def f():
+            def g():
+                return "value"
+            return g
+
+        f_code = Bytecode.from_code(f.__code__)
+        instr_load_code = None
+        mutable_datum = [4, 2]
+
+        for each in f_code:
+            if (isinstance(each, Instr)
+               and each.name == 'LOAD_CONST'
+               and isinstance(each.arg, CodeType)):
+                instr_load_code = each
+                break
+
+        self.assertIsNotNone(instr_load_code)
+
+        g_code = Bytecode.from_code(instr_load_code.arg)
+        g_code[0].arg = mutable_datum
+        instr_load_code.arg = g_code.to_code()
+        f.__code__ = f_code.to_code()
+
+        self.assertIs(f()(), mutable_datum)
+
 
 if __name__ == "__main__":
     unittest.main()

doc/changelog.rst

@@ -11,6 +11,10 @@ New features:
 - :class:`Bytecode`, :class:`ConcreteBytecode`, :class:`BasicBlock` and 
   :class:`ControlFlowGraph` have a new :meth:`legalize` method validating 
   their content and removing SetLineno. PR #52
+- Modify the implementation of :code:`const_key` to avoid manual
+  synchronizations with :code:`_PyCode_ConstantKey` in CPython codebase and
+  allow the use of arbitrary Python objects as constants of nested code
+  objects. #54
 
 API changes: