"""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.