Move session-related code to new session module

[leogama]

Edit: updated.

Here is the relevant segment of the diff between the old _dill.py and the new session.py:

--- old/_dill.py	2022-07-22 14:13:01.157703539 -0300
+++ dill/session.py	2022-07-22 14:09:18.306036272 -0300
@@ -1,339 +1,43 @@
-# -*- coding: utf-8 -*-
+#!/usr/bin/env python
 #
 # Author: Mike McKerns (mmckerns @caltech and @uqfoundation)
+# Author: Leonardo Gama (@leogama)
 # Copyright (c) 2008-2015 California Institute of Technology.
 # Copyright (c) 2016-2022 The Uncertainty Quantification Foundation.
 # License: 3-clause BSD.  The full license text is available at:
 #  - https://github.com/uqfoundation/dill/blob/master/LICENSE
 """
-dill: a utility for serialization of python objects
-
-Based on code written by Oren Tirosh and Armin Ronacher.
-Extended to a (near) full set of the builtin types (in types module),
-and coded to the pickle interface, by <mmckerns@caltech.edu>.
-Initial port to python3 by Jonathan Dobson, continued by mmckerns.
-Test against "all" python types (Std. Lib. CH 1-15 @ 2.7) by mmckerns.
-Test against CH16+ Std. Lib. ... TBD.
+Pickle and restore the intepreter session.
 """
+
 __all__ = [
-    'dump', 'dumps', 'load', 'loads', 'dump_module', 'load_module',
-    'load_module_asdict', 'dump_session', 'load_session', 'Pickler', 'Unpickler',
-    'register', 'copy', 'pickle', 'pickles', 'check', 'HIGHEST_PROTOCOL',
-    'DEFAULT_PROTOCOL', 'PicklingError', 'UnpicklingError', 'HANDLE_FMODE',
-    'CONTENTS_FMODE', 'FILE_FMODE', 'PickleError', 'PickleWarning',
-    'PicklingWarning', 'UnpicklingWarning'
+    'dump_module', 'load_module', 'load_module_asdict',
+    'dump_session', 'load_session' # backward compatibility
 ]
 
-__module__ = 'dill'
-
-import warnings
-from .logger import adapter as logger
-from .logger import trace as _trace
-
-from typing import Optional, Union
-
-import os
+import re
 import sys
-----------------------------------<omitted>------------------------------------
+import warnings
+ 
+from dill import _dill, Pickler, Unpickler
+from ._dill import (
+    BuiltinMethodType, FunctionType, MethodType, ModuleType, TypeType,
+    _import_module, _is_builtin_module, _is_imported_module, _main_module,
+    _reverse_typemap, __builtin__,
+)
 
+# Type hints.
+from typing import Optional, Union
 
-### Pickle the Interpreter Session
 import pathlib
-import re
 import tempfile
-from types import SimpleNamespace
 
 TEMPDIR = pathlib.PurePath(tempfile.gettempdir())
 
 def _module_map():
     """get map of imported modules"""
     from collections import defaultdict
+    from types import SimpleNamespace
     modmap = SimpleNamespace(
         by_name=defaultdict(list),
         by_id=defaultdict(list),
@@ -349,10 +53,12 @@
             modmap.by_id[id(modobj)].append((modobj, objname, modname))
     return modmap
 
-SESSION_IMPORTED_AS_TYPES = (ModuleType, TypeType, FunctionType, MethodType, BuiltinMethodType)
-SESSION_IMPORTED_AS_MODULES = ('ctypes', 'typing', 'subprocess', 'threading',
+IMPORTED_AS_TYPES = (ModuleType, TypeType, FunctionType, MethodType, BuiltinMethodType)
+if 'PyCapsuleType' in _reverse_typemap:
+    IMPORTED_AS_TYPES += (_reverse_typemap['PyCapsuleType'],)
+IMPORTED_AS_MODULES = ('ctypes', 'typing', 'subprocess', 'threading',
                                r'concurrent\.futures(\.\w+)?', r'multiprocessing(\.\w+)?')
-SESSION_IMPORTED_AS_MODULES = tuple(re.compile(x) for x in SESSION_IMPORTED_AS_MODULES)
+IMPORTED_AS_MODULES = tuple(re.compile(x) for x in IMPORTED_AS_MODULES)
 
 def _lookup_module(modmap, name, obj, main_module):
     """lookup name or id of obj if module is imported"""
@@ -360,8 +66,8 @@
         if modobj is obj and sys.modules[modname] is not main_module:
             return modname, name
     __module__ = getattr(obj, '__module__', None)
-    if isinstance(obj, SESSION_IMPORTED_AS_TYPES) or (__module__ is not None
-            and any(regex.fullmatch(__module__) for regex in SESSION_IMPORTED_AS_MODULES)):
+    if isinstance(obj, IMPORTED_AS_TYPES) or (__module__ is not None
+            and any(regex.fullmatch(__module__) for regex in IMPORTED_AS_MODULES)):
         for modobj, objname, modname in modmap.by_id[id(obj)]:
             if sys.modules[modname] is not main_module:
                 return modname, objname
@@ -838,6 +544,7 @@
         >>> new_var in main # would be True if the option 'update' was set
         False
     """
     if 'module' in kwds:
         raise TypeError("'module' is an invalid keyword argument for load_module_asdict()")
     if hasattr(filename, 'read'):
@@ -869,1729 +576,3 @@
             pass
     main.__session__ = str(filename)
     return main.__dict__
-
-### End: Pickle the Interpreter
-----------------------------------<omitted>------------------------------------

[mmckerns]

I have three thoughts, even before reviewing: (1) you should make sure there are backward compatible imports for anything that you've moved to a new module, (2) would it be better to use main.__builtins__ = __builtins__ instead of importing builtins? (although it's probably a negligible difference), (3) the new module would need to be added to docs/source/dill.rst.

[leogama]

(1) you should make sure there are backward compatible imports for anything that you've moved to a new module

I was thinking about this just now.

(2) would it be better to use main.__builtins__ = __builtins__ instead of importing builtins? (although it's probably a negligible difference)

May be. I'll change this.

(3) the new module would need to be added to docs/source/dill.rst.

Already did that.

[leogama]

(1) you should make sure there are backward compatible imports for anything that you've moved to a new module

I was thinking about this just now.

There's a problem with this though. Adding from .session import * at the top of dill._dill will create circular import problems. I'll probably have to add it at the bottom. Actually, I had to export to dill._dill at the end of dill.session.

Should I include 'dump_session' and 'load_session' in dill._dill.__all__?

[leogama]

@mmckerns: applied the requested changes.

[mmckerns]

LGTM