"""Helper to provide extensibility for pickle/cPickle. This is only useful to add pickle support for extension types defined inC, 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     # 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:    complexexcept NameError:    passelse:     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)        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    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:        if getattr(self, "__slots__", None):            raise TypeError("a class that defines __slots__ without "                            "defining __getstate__ cannot be pickled")        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 _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, basestring):                    slots = (slots,)                for name in slots:                    # special descriptors                    if name in ("__dict__", "__weakref__"):                        continue                    # mangled names                    elif name.startswith('__') and not name.endswith('__'):                        names.append('_%s%s' % (c.__name__, 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:  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.