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