Lib/copy_reg.py

   1 """Helper to provide extensibility for pickle/cPickle.
   2
   3 This is only useful to add pickle support for extension types defined in
   4 C, not for instances of user-defined classes.
   5 """
   6
   7 from types import ClassType as _ClassType
   8
   9 __all__ = ["pickle", "constructor",
  10            "add_extension", "remove_extension", "clear_extension_cache"]
  11
  12 dispatch_table = {}
  13
  14 def pickle(ob_type, pickle_function, constructor_ob=None):
  15     if type(ob_type) is _ClassType:
  16         raise TypeError("copy_reg is not intended for use with classes")
  17
  18     if not callable(pickle_function):
  19         raise TypeError("reduction functions must be callable")
  20     dispatch_table[ob_type] = pickle_function
  21
  22     # The constructor_ob function is a vestige of safe for unpickling.
  23     # There is no reason for the caller to pass it anymore.
  24     if constructor_ob is not None:
  25         constructor(constructor_ob)
  26
  27 def constructor(object):
  28     if not callable(object):
  29         raise TypeError("constructors must be callable")
  30
  31 # Example: provide pickling support for complex numbers.
  32
  33 try:
  34     complex
  35 except NameError:
  36     pass
  37 else:
  38
  39     def pickle_complex(c):
  40         return complex, (c.real, c.imag)
  41
  42     pickle(complex, pickle_complex, complex)
  43
  44 # Support for pickling new-style objects
  45
  46 def _reconstructor(cls, base, state):
  47     if base is object:
  48         obj = object.__new__(cls)
  49     else:
  50         obj = base.__new__(cls, state)
  51         base.__init__(obj, state)
  52     return obj
  53
  54 _HEAPTYPE = 1<<9
  55
  56 # Python code for object.__reduce_ex__ for protocols 0 and 1
  57
  58 def _reduce_ex(self, proto):
  59     assert proto < 2
  60     for base in self.__class__.__mro__:
  61         if hasattr(base, '__flags__') and not base.__flags__ & _HEAPTYPE:
  62             break
  63     else:
  64         base = object # not really reachable
  65     if base is object:
  66         state = None
  67     else:
  68         if base is self.__class__:
  69             raise TypeError, "can't pickle %s objects" % base.__name__
  70         state = base(self)
  71     args = (self.__class__, base, state)
  72     try:
  73         getstate = self.__getstate__
  74     except AttributeError:
  75         if getattr(self, "__slots__", None):
  76             raise TypeError("a class that defines __slots__ without "
  77                             "defining __getstate__ cannot be pickled")
  78         try:
  79             dict = self.__dict__
  80         except AttributeError:
  81             dict = None
  82     else:
  83         dict = getstate()
  84     if dict:
  85         return _reconstructor, args, dict
  86     else:
  87         return _reconstructor, args
  88
  89 # Helper for __reduce_ex__ protocol 2
  90
  91 def __newobj__(cls, *args):
  92     return cls.__new__(cls, *args)
  93
  94 def _slotnames(cls):
  95     """Return a list of slot names for a given class.
  96
  97     This needs to find slots defined by the class and its bases, so we
  98     can't simply return the __slots__ attribute.  We must walk down
  99     the Method Resolution Order and concatenate the __slots__ of each
 100     class found there.  (This assumes classes don't modify their
 101     __slots__ attribute to misrepresent their slots after the class is
 102     defined.)
 103     """
 104
 105     # Get the value from a cache in the class if possible
 106     names = cls.__dict__.get("__slotnames__")
 107     if names is not None:
 108         return names
 109
 110     # Not cached -- calculate the value
 111     names = []
 112     if not hasattr(cls, "__slots__"):
 113         # This class has no slots
 114         pass
 115     else:
 116         # Slots found -- gather slot names from all base classes
 117         for c in cls.__mro__:
 118             if "__slots__" in c.__dict__:
 119                 slots = c.__dict__['__slots__']
 120                 # if class has a single slot, it can be given as a string
 121                 if isinstance(slots, basestring):
 122                     slots = (slots,)
 123                 for name in slots:
 124                     # special descriptors
 125                     if name in ("__dict__", "__weakref__"):
 126                         continue
 127                     # mangled names
 128                     elif name.startswith('__') and not name.endswith('__'):
 129                         names.append('_%s%s' % (c.__name__, name))
 130                     else:
 131                         names.append(name)
 132
 133     # Cache the outcome in the class if at all possible
 134     try:
 135         cls.__slotnames__ = names
 136     except:
 137         pass # But don't die if we can't
 138
 139     return names
 140
 141 # A registry of extension codes.  This is an ad-hoc compression
 142 # mechanism.  Whenever a global reference to <module>, <name> is about
 143 # to be pickled, the (<module>, <name>) tuple is looked up here to see
 144 # if it is a registered extension code for it.  Extension codes are
 145 # universal, so that the meaning of a pickle does not depend on
 146 # context.  (There are also some codes reserved for local use that
 147 # don't have this restriction.)  Codes are positive ints; 0 is
 148 # reserved.
 149
 150 _extension_registry = {}                # key -> code
 151 _inverted_registry = {}                 # code -> key
 152 _extension_cache = {}                   # code -> object
 153 # Don't ever rebind those names:  cPickle grabs a reference to them when
 154 # it's initialized, and won't see a rebinding.
 155
 156 def add_extension(module, name, code):
 157     """Register an extension code."""
 158     code = int(code)
 159     if not 1 <= code <= 0x7fffffff:
 160         raise ValueError, "code out of range"
 161     key = (module, name)
 162     if (_extension_registry.get(key) == code and
 163         _inverted_registry.get(code) == key):
 164         return # Redundant registrations are benign
 165     if key in _extension_registry:
 166         raise ValueError("key %s is already registered with code %s" %
 167                          (key, _extension_registry[key]))
 168     if code in _inverted_registry:
 169         raise ValueError("code %s is already in use for key %s" %
 170                          (code, _inverted_registry[code]))
 171     _extension_registry[key] = code
 172     _inverted_registry[code] = key
 173
 174 def remove_extension(module, name, code):
 175     """Unregister an extension code.  For testing only."""
 176     key = (module, name)
 177     if (_extension_registry.get(key) != code or
 178         _inverted_registry.get(code) != key):
 179         raise ValueError("key %s is not registered with code %s" %
 180                          (key, code))
 181     del _extension_registry[key]
 182     del _inverted_registry[code]
 183     if code in _extension_cache:
 184         del _extension_cache[code]
 185
 186 def clear_extension_cache():
 187     _extension_cache.clear()
 188
 189 # Standard extension code assignments
 190
 191 # Reserved ranges
 192
 193 # First  Last Count  Purpose
 194 #     1   127   127  Reserved for Python standard library
 195 #   128   191    64  Reserved for Zope
 196 #   192   239    48  Reserved for 3rd parties
 197 #   240   255    16  Reserved for private use (will never be assigned)
 198 #   256   Inf   Inf  Reserved for future assignment
 199
 200 # Extension codes are assigned by the Python Software Foundation.