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copyreg.py
"""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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