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"""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

_new_type = type(int.__new__)

# 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

new = base.__new__

if isinstance(new, _new_type) and new.__self__ is base:

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.

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