Lib/copy_reg.py

"""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.