"""Helper to provide extensibility for pickle.
This is only useful to add pickle support for extension types defined in
C, not for instances of user-defined classes.
"""
__all__ = ["pickle", "constructor",
"add_extension", "remove_extension", "clear_extension_cache"]
dispatch_table = {}
def pickle(ob_type, pickle_function, constructor_ob=None):
if not callable(pickle_function):
raise TypeError("reduction functions must be callable")
dispatch_table[ob_type] = pickle_function
# The constructor_ob function is a vestige of safe for unpickling.
# There is no reason for the caller to pass it anymore.
if constructor_ob is not None:
constructor(constructor_ob)
def constructor(object):
if not callable(object):
raise TypeError("constructors must be callable")
# Example: provide pickling support for complex numbers.
try:
complex
except NameError:
pass
else:
def pickle_complex(c):
return complex, (c.real, c.imag)
pickle(complex, pickle_complex, complex)
# Support for pickling new-style objects
def _reconstructor(cls, base, state):
if base is object:
obj = object.__new__(cls)
else:
obj = base.__new__(cls, state)
if base.__init__ != object.__init__:
base.__init__(obj, state)
return obj
_HEAPTYPE = 1<<9
# Python code for object.__reduce_ex__ for protocols 0 and 1
def _reduce_ex(self, proto):
assert proto < 2
cls = self.__class__
for base in cls.__mro__:
if hasattr(base, '__flags__') and not base.__flags__ & _HEAPTYPE:
break
else:
base = object # not really reachable
if base is object:
state = None
else:
if base is cls:
raise TypeError(f"cannot pickle {cls.__name__!r} object")
state = base(self)
args = (cls, base, state)
try:
getstate = self.__getstate__
except AttributeError:
if getattr(self, "__slots__", None):
raise TypeError(f"cannot pickle {cls.__name__!r} object: "
f"a class that defines __slots__ without "
f"defining __getstate__ cannot be pickled "
f"with protocol {proto}") from None
try:
dict = self.__dict__
except AttributeError:
dict = None
else:
dict = getstate()
if dict:
return _reconstructor, args, dict
else:
return _reconstructor, args
# Helper for __reduce_ex__ protocol 2
def __newobj__(cls, *args):
return cls.__new__(cls, *args)
def __newobj_ex__(cls, args, kwargs):
"""Used by pickle protocol 4, instead of __newobj__ to allow classes with
keyword-only arguments to be pickled correctly.
"""
return cls.__new__(cls, *args, **kwargs)
def _slotnames(cls):
"""Return a list of slot names for a given class.
This needs to find slots defined by the class and its bases, so we
can't simply return the __slots__ attribute. We must walk down
the Method Resolution Order and concatenate the __slots__ of each
class found there. (This assumes classes don't modify their
__slots__ attribute to misrepresent their slots after the class is
defined.)
"""
# Get the value from a cache in the class if possible
names = cls.__dict__.get("__slotnames__")
if names is not None:
return names
# Not cached -- calculate the value
names = []
if not hasattr(cls, "__slots__"):
# This class has no slots
pass
else:
# Slots found -- gather slot names from all base classes
for c in cls.__mro__:
if "__slots__" in c.__dict__:
slots = c.__dict__['__slots__']
# if class has a single slot, it can be given as a string
if isinstance(slots, str):
slots = (slots,)
for name in slots:
# special descriptors
if name in ("__dict__", "__weakref__"):
continue
# mangled names
elif name.startswith('__') and not name.endswith('__'):
stripped = c.__name__.lstrip('_')
if stripped:
names.append('_%s%s' % (stripped, name))
else:
names.append(name)
else:
names.append(name)
# Cache the outcome in the class if at all possible
try:
cls.__slotnames__ = names
except:
pass # But don't die if we can't
return names
# A registry of extension codes. This is an ad-hoc compression
# mechanism. Whenever a global reference to <module>, <name> is about
# to be pickled, the (<module>, <name>) tuple is looked up here to see
# if it is a registered extension code for it. Extension codes are
# universal, so that the meaning of a pickle does not depend on
# context. (There are also some codes reserved for local use that
# don't have this restriction.) Codes are positive ints; 0 is
# reserved.
_extension_registry = {} # key -> code
_inverted_registry = {} # code -> key
_extension_cache = {} # code -> object
# Don't ever rebind those names: pickling grabs a reference to them when
# it's initialized, and won't see a rebinding.
def add_extension(module, name, code):
"""Register an extension code."""
code = int(code)
if not 1 <= code <= 0x7fffffff:
raise ValueError("code out of range")
key = (module, name)
if (_extension_registry.get(key) == code and
_inverted_registry.get(code) == key):
return # Redundant registrations are benign
if key in _extension_registry:
raise ValueError("key %s is already registered with code %s" %
(key, _extension_registry[key]))
if code in _inverted_registry:
raise ValueError("code %s is already in use for key %s" %
(code, _inverted_registry[code]))
_extension_registry[key] = code
_inverted_registry[code] = key
def remove_extension(module, name, code):
"""Unregister an extension code. For testing only."""
key = (module, name)
if (_extension_registry.get(key) != code or
_inverted_registry.get(code) != key):
raise ValueError("key %s is not registered with code %s" %
(key, code))
del _extension_registry[key]
del _inverted_registry[code]
if code in _extension_cache:
del _extension_cache[code]
def clear_extension_cache():
_extension_cache.clear()
# Standard extension code assignments
# Reserved ranges
# First Last Count Purpose
# 1 127 127 Reserved for Python standard library
# 128 191 64 Reserved for Zope
# 192 239 48 Reserved for 3rd parties
# 240 255 16 Reserved for private use (will never be assigned)
# 256 Inf Inf Reserved for future assignment
# Extension codes are assigned by the Python Software Foundation.
