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"""Helper to provide extensibility for pickle/cPickle.
This is only useful to add pickle support for extension types defined in
C, not for instances of user-defined classes.
"""
from types import ClassType as _ClassType
__all__ = ["pickle", "constructor",
"add_extension", "remove_extension", "clear_extension_cache"]
dispatch_table = {}
def pickle(ob_type, pickle_function, constructor_ob=None):
if type(ob_type) is _ClassType:
raise TypeError("copy_reg is not intended for use with classes")
if not callable(pickle_function):
raise TypeError("reduction functions must be callable")
dispatch_table[ob_type] = pickle_function
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.
def pickle_complex(c):
return complex, (c.real, c.imag)
pickle(type(1j), pickle_complex, complex)
# Support for picking new-style objects
def _reconstructor(cls, base, state):
obj = base.__new__(cls, state)
base.__init__(obj, state)
return obj
_HEAPTYPE = 1<<9
def _reduce(self):
for base in self.__class__.__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 self.__class__:
raise TypeError, "can't pickle %s objects" % base.__name__
state = base(self)
args = (self.__class__, base, state)
try:
getstate = self.__getstate__
except AttributeError:
try:
dict = self.__dict__
except AttributeError:
dict = None
else:
dict = getstate()
if dict:
return _reconstructor, args, dict
else:
return _reconstructor, args
# A better version of _reduce, used by copy and pickle protocol 2
def __newobj__(cls, *args):
return cls.__new__(cls, *args)
def _better_reduce(obj):
cls = obj.__class__
getnewargs = getattr(obj, "__getnewargs__", None)
if getnewargs:
args = getnewargs()
else:
args = ()
getstate = getattr(obj, "__getstate__", None)
if getstate:
try:
state = getstate()
except TypeError, err:
# XXX Catch generic exception caused by __slots__
if str(err) != ("a class that defines __slots__ "
"without defining __getstate__ "
"cannot be pickled"):
raise # Not that specific exception
getstate = None
if not getstate:
state = getattr(obj, "__dict__", None)
names = _slotnames(cls)
if names:
slots = {}
nil = []
for name in names:
value = getattr(obj, name, nil)
if value is not nil:
slots[name] = value
if slots:
state = (state, slots)
listitems = dictitems = None
if isinstance(obj, list):
listitems = iter(obj)
elif isinstance(obj, dict):
dictitems = obj.iteritems()
return __newobj__, (cls,) + args, state, listitems, dictitems
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__:
names += [name for name in c.__dict__["__slots__"]
if name not in ("__dict__", "__weakref__")]
# 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: cPickle 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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