Prepare transition to let cloudpickle.Pickler point to CloudPickler

cloudpickle/__init__.py

@@ -2,9 +2,34 @@
 
 import sys
 import pickle
+import types
+import warnings
 
+import cloudpickle.cloudpickle as cp
+
+
+class CustomModuleType(types.ModuleType):
+    def __getattr__(self, name):
+        if name == 'Pickler':
+            warnings.warn(
+                'Pickler will point to Cloudpickler in two releases.',
+                FutureWarning
+            )
+            return self._Pickler
+        raise AttributeError
+
+    def __reduce__(self):
+        return __import__, ("cloudpickle.cloudpickle",)
+
+
+cp.__class__ = CustomModuleType
+
+if sys.version_info[:2] >= (3, 7):
+    def __getattr__(name):
+        return cp.__class__.__getattr__(cp, name)
 
 from cloudpickle.cloudpickle import *
+
 if sys.version_info[:2] >= (3, 8):
     from cloudpickle.cloudpickle_fast import CloudPickler, dumps, dump
 

cloudpickle/cloudpickle.py

@@ -62,7 +62,7 @@
 from enum import Enum
 
 from typing import Generic, Union, Tuple, Callable
-from pickle import _Pickler as Pickler
+from pickle import _Pickler
 from pickle import _getattribute
 from io import BytesIO
 from importlib._bootstrap import _find_spec
@@ -460,21 +460,21 @@ def _create_parametrized_type_hint(origin, args):
         return origin[args]
 
 
-class CloudPickler(Pickler):
+class CloudPickler(_Pickler):
 
-    dispatch = Pickler.dispatch.copy()
+    dispatch = _Pickler.dispatch.copy()
 
     def __init__(self, file, protocol=None):
         if protocol is None:
             protocol = DEFAULT_PROTOCOL
-        Pickler.__init__(self, file, protocol=protocol)
+        _Pickler.__init__(self, file, protocol=protocol)
         # map ids to dictionary. used to ensure that functions can share global env
         self.globals_ref = {}
 
     def dump(self, obj):
         self.inject_addons()
         try:
-            return Pickler.dump(self, obj)
+            return _Pickler.dump(self, obj)
         except RuntimeError as e:
             if 'recursion' in e.args[0]:
                 msg = """Could not pickle object as excessively deep recursion required."""
@@ -537,7 +537,7 @@ def save_function(self, obj, name=None):
         interactive prompt, etc) and handles the pickling appropriately.
         """
         if _is_importable_by_name(obj, name=name):
-            return Pickler.save_global(self, obj, name=name)
+            return _Pickler.save_global(self, obj, name=name)
         elif PYPY and isinstance(obj.__code__, builtin_code_type):
             return self.save_pypy_builtin_func(obj)
         else:
@@ -839,11 +839,11 @@ def save_global(self, obj, name=None, pack=struct.pack):
             # dispatch with type-specific savers.
             self._save_parametrized_type_hint(obj)
         elif name is not None:
-            Pickler.save_global(self, obj, name=name)
+            _Pickler.save_global(self, obj, name=name)
         elif not _is_importable_by_name(obj, name=name):
             self.save_dynamic_class(obj)
         else:
-            Pickler.save_global(self, obj, name=name)
+            _Pickler.save_global(self, obj, name=name)
 
     dispatch[type] = save_global
 

tests/cloudpickle_test.py

@@ -23,6 +23,7 @@
 import os
 import enum
 import typing
+import warnings
 from functools import wraps
 
 import pytest
@@ -56,6 +57,20 @@
 _TEST_GLOBAL_VARIABLE = "default_value"
 
 
+def test_future_warning_pickler():
+    # FutureWarning should be raised when accessing Pickler
+    with warnings.catch_warnings(record=True) as warning:
+        warnings.simplefilter("always")
+        pickler = cloudpickle.Pickler
+        assert len(warning) == 1
+        assert issubclass(warning[-1].category, FutureWarning)
+        assert "Pickler will point to Cloudpickler in two releases." \
+            in str(warning[-1].message)
+
+    # cloudpickle.Pickler should still be pointing to pickle._Pickler
+    assert pickler == pickle._Pickler
+
+
 class RaiserOnPickle(object):
 
     def __init__(self, exc):