Lib/copy.py

   1 """Generic (shallow and deep) copying operations.
   2
   3 Interface summary:
   4
   5         import copy
   6
   7         x = copy.copy(y)        # make a shallow copy of y
   8         x = copy.deepcopy(y)    # make a deep copy of y
   9
  10 For module specific errors, copy.Error is raised.
  11
  12 The difference between shallow and deep copying is only relevant for
  13 compound objects (objects that contain other objects, like lists or
  14 class instances).
  15
  16 - A shallow copy constructs a new compound object and then (to the
  17   extent possible) inserts *the same objects* into it that the
  18   original contains.
  19
  20 - A deep copy constructs a new compound object and then, recursively,
  21   inserts *copies* into it of the objects found in the original.
  22
  23 Two problems often exist with deep copy operations that don't exist
  24 with shallow copy operations:
  25
  26  a) recursive objects (compound objects that, directly or indirectly,
  27     contain a reference to themselves) may cause a recursive loop
  28
  29  b) because deep copy copies *everything* it may copy too much, e.g.
  30     administrative data structures that should be shared even between
  31     copies
  32
  33 Python's deep copy operation avoids these problems by:
  34
  35  a) keeping a table of objects already copied during the current
  36     copying pass
  37
  38  b) letting user-defined classes override the copying operation or the
  39     set of components copied
  40
  41 This version does not copy types like module, class, function, method,
  42 nor stack trace, stack frame, nor file, socket, window, nor array, nor
  43 any similar types.
  44
  45 Classes can use the same interfaces to control copying that they use
  46 to control pickling: they can define methods called __getinitargs__(),
  47 __getstate__() and __setstate__().  See the documentation for module
  48 "pickle" for information on these methods.
  49 """
  50
  51 import types
  52 import weakref
  53 from copy_reg import dispatch_table
  54
  55 class Error(Exception):
  56     pass
  57 error = Error   # backward compatibility
  58
  59 try:
  60     from org.python.core import PyStringMap
  61 except ImportError:
  62     PyStringMap = None
  63
  64 __all__ = ["Error", "copy", "deepcopy"]
  65
  66 def copy(x):
  67     """Shallow copy operation on arbitrary Python objects.
  68
  69     See the module's __doc__ string for more info.
  70     """
  71
  72     cls = type(x)
  73
  74     copier = _copy_dispatch.get(cls)
  75     if copier:
  76         return copier(x)
  77
  78     copier = getattr(cls, "__copy__", None)
  79     if copier:
  80         return copier(x)
  81
  82     reductor = dispatch_table.get(cls)
  83     if reductor:
  84         rv = reductor(x)
  85     else:
  86         reductor = getattr(x, "__reduce_ex__", None)
  87         if reductor:
  88             rv = reductor(2)
  89         else:
  90             reductor = getattr(x, "__reduce__", None)
  91             if reductor:
  92                 rv = reductor()
  93             else:
  94                 raise Error("un(shallow)copyable object of type %s" % cls)
  95
  96     return _reconstruct(x, rv, 0)
  97
  98
  99 _copy_dispatch = d = {}
 100
 101 def _copy_immutable(x):
 102     return x
 103 for t in (type(None), int, long, float, bool, str, tuple,
 104           frozenset, type, xrange, types.ClassType,
 105           types.BuiltinFunctionType, type(Ellipsis),
 106           types.FunctionType, weakref.ref):
 107     d[t] = _copy_immutable
 108 for name in ("ComplexType", "UnicodeType", "CodeType"):
 109     t = getattr(types, name, None)
 110     if t is not None:
 111         d[t] = _copy_immutable
 112
 113 def _copy_with_constructor(x):
 114     return type(x)(x)
 115 for t in (list, dict, set):
 116     d[t] = _copy_with_constructor
 117
 118 def _copy_with_copy_method(x):
 119     return x.copy()
 120 if PyStringMap is not None:
 121     d[PyStringMap] = _copy_with_copy_method
 122
 123 def _copy_inst(x):
 124     if hasattr(x, '__copy__'):
 125         return x.__copy__()
 126     if hasattr(x, '__getinitargs__'):
 127         args = x.__getinitargs__()
 128         y = x.__class__(*args)
 129     else:
 130         y = _EmptyClass()
 131         y.__class__ = x.__class__
 132     if hasattr(x, '__getstate__'):
 133         state = x.__getstate__()
 134     else:
 135         state = x.__dict__
 136     if hasattr(y, '__setstate__'):
 137         y.__setstate__(state)
 138     else:
 139         y.__dict__.update(state)
 140     return y
 141 d[types.InstanceType] = _copy_inst
 142
 143 del d
 144
 145 def deepcopy(x, memo=None, _nil=[]):
 146     """Deep copy operation on arbitrary Python objects.
 147
 148     See the module's __doc__ string for more info.
 149     """
 150
 151     if memo is None:
 152         memo = {}
 153
 154     d = id(x)
 155     y = memo.get(d, _nil)
 156     if y is not _nil:
 157         return y
 158
 159     cls = type(x)
 160
 161     copier = _deepcopy_dispatch.get(cls)
 162     if copier:
 163         y = copier(x, memo)
 164     else:
 165         try:
 166             issc = issubclass(cls, type)
 167         except TypeError: # cls is not a class (old Boost; see SF #502085)
 168             issc = 0
 169         if issc:
 170             y = _deepcopy_atomic(x, memo)
 171         else:
 172             copier = getattr(x, "__deepcopy__", None)
 173             if copier:
 174                 y = copier(memo)
 175             else:
 176                 reductor = dispatch_table.get(cls)
 177                 if reductor:
 178                     rv = reductor(x)
 179                 else:
 180                     reductor = getattr(x, "__reduce_ex__", None)
 181                     if reductor:
 182                         rv = reductor(2)
 183                     else:
 184                         reductor = getattr(x, "__reduce__", None)
 185                         if reductor:
 186                             rv = reductor()
 187                         else:
 188                             raise Error(
 189                                 "un(deep)copyable object of type %s" % cls)
 190                 y = _reconstruct(x, rv, 1, memo)
 191
 192     memo[d] = y
 193     _keep_alive(x, memo) # Make sure x lives at least as long as d
 194     return y
 195
 196 _deepcopy_dispatch = d = {}
 197
 198 def _deepcopy_atomic(x, memo):
 199     return x
 200 d[type(None)] = _deepcopy_atomic
 201 d[type(Ellipsis)] = _deepcopy_atomic
 202 d[int] = _deepcopy_atomic
 203 d[long] = _deepcopy_atomic
 204 d[float] = _deepcopy_atomic
 205 d[bool] = _deepcopy_atomic
 206 try:
 207     d[complex] = _deepcopy_atomic
 208 except NameError:
 209     pass
 210 d[str] = _deepcopy_atomic
 211 try:
 212     d[unicode] = _deepcopy_atomic
 213 except NameError:
 214     pass
 215 try:
 216     d[types.CodeType] = _deepcopy_atomic
 217 except AttributeError:
 218     pass
 219 d[type] = _deepcopy_atomic
 220 d[xrange] = _deepcopy_atomic
 221 d[types.ClassType] = _deepcopy_atomic
 222 d[types.BuiltinFunctionType] = _deepcopy_atomic
 223 d[types.FunctionType] = _deepcopy_atomic
 224 d[weakref.ref] = _deepcopy_atomic
 225
 226 def _deepcopy_list(x, memo):
 227     y = []
 228     memo[id(x)] = y
 229     for a in x:
 230         y.append(deepcopy(a, memo))
 231     return y
 232 d[list] = _deepcopy_list
 233
 234 def _deepcopy_tuple(x, memo):
 235     y = []
 236     for a in x:
 237         y.append(deepcopy(a, memo))
 238     d = id(x)
 239     try:
 240         return memo[d]
 241     except KeyError:
 242         pass
 243     for i in range(len(x)):
 244         if x[i] is not y[i]:
 245             y = tuple(y)
 246             break
 247     else:
 248         y = x
 249     memo[d] = y
 250     return y
 251 d[tuple] = _deepcopy_tuple
 252
 253 def _deepcopy_dict(x, memo):
 254     y = {}
 255     memo[id(x)] = y
 256     for key, value in x.iteritems():
 257         y[deepcopy(key, memo)] = deepcopy(value, memo)
 258     return y
 259 d[dict] = _deepcopy_dict
 260 if PyStringMap is not None:
 261     d[PyStringMap] = _deepcopy_dict
 262
 263 def _keep_alive(x, memo):
 264     """Keeps a reference to the object x in the memo.
 265
 266     Because we remember objects by their id, we have
 267     to assure that possibly temporary objects are kept
 268     alive by referencing them.
 269     We store a reference at the id of the memo, which should
 270     normally not be used unless someone tries to deepcopy
 271     the memo itself...
 272     """
 273     try:
 274         memo[id(memo)].append(x)
 275     except KeyError:
 276         # aha, this is the first one :-)
 277         memo[id(memo)]=[x]
 278
 279 def _deepcopy_inst(x, memo):
 280     if hasattr(x, '__deepcopy__'):
 281         return x.__deepcopy__(memo)
 282     if hasattr(x, '__getinitargs__'):
 283         args = x.__getinitargs__()
 284         args = deepcopy(args, memo)
 285         y = x.__class__(*args)
 286     else:
 287         y = _EmptyClass()
 288         y.__class__ = x.__class__
 289     memo[id(x)] = y
 290     if hasattr(x, '__getstate__'):
 291         state = x.__getstate__()
 292     else:
 293         state = x.__dict__
 294     state = deepcopy(state, memo)
 295     if hasattr(y, '__setstate__'):
 296         y.__setstate__(state)
 297     else:
 298         y.__dict__.update(state)
 299     return y
 300 d[types.InstanceType] = _deepcopy_inst
 301
 302 def _reconstruct(x, info, deep, memo=None):
 303     if isinstance(info, str):
 304         return x
 305     assert isinstance(info, tuple)
 306     if memo is None:
 307         memo = {}
 308     n = len(info)
 309     assert n in (2, 3, 4, 5)
 310     callable, args = info[:2]
 311     if n > 2:
 312         state = info[2]
 313     else:
 314         state = {}
 315     if n > 3:
 316         listiter = info[3]
 317     else:
 318         listiter = None
 319     if n > 4:
 320         dictiter = info[4]
 321     else:
 322         dictiter = None
 323     if deep:
 324         args = deepcopy(args, memo)
 325     y = callable(*args)
 326     memo[id(x)] = y
 327     if listiter is not None:
 328         for item in listiter:
 329             if deep:
 330                 item = deepcopy(item, memo)
 331             y.append(item)
 332     if dictiter is not None:
 333         for key, value in dictiter:
 334             if deep:
 335                 key = deepcopy(key, memo)
 336                 value = deepcopy(value, memo)
 337             y[key] = value
 338     if state:
 339         if deep:
 340             state = deepcopy(state, memo)
 341         if hasattr(y, '__setstate__'):
 342             y.__setstate__(state)
 343         else:
 344             if isinstance(state, tuple) and len(state) == 2:
 345                 state, slotstate = state
 346             else:
 347                 slotstate = None
 348             if state is not None:
 349                 y.__dict__.update(state)
 350             if slotstate is not None:
 351                 for key, value in slotstate.iteritems():
 352                     setattr(y, key, value)
 353     return y
 354
 355 del d
 356
 357 del types
 358
 359 # Helper for instance creation without calling __init__
 360 class _EmptyClass:
 361     pass
 362
 363 def _test():
 364     l = [None, 1, 2L, 3.14, 'xyzzy', (1, 2L), [3.14, 'abc'],
 365          {'abc': 'ABC'}, (), [], {}]
 366     l1 = copy(l)
 367     print l1==l
 368     l1 = map(copy, l)
 369     print l1==l
 370     l1 = deepcopy(l)
 371     print l1==l
 372     class C:
 373         def __init__(self, arg=None):
 374             self.a = 1
 375             self.arg = arg
 376             if __name__ == '__main__':
 377                 import sys
 378                 file = sys.argv[0]
 379             else:
 380                 file = __file__
 381             self.fp = open(file)
 382             self.fp.close()
 383         def __getstate__(self):
 384             return {'a': self.a, 'arg': self.arg}
 385         def __setstate__(self, state):
 386             for key, value in state.iteritems():
 387                 setattr(self, key, value)
 388         def __deepcopy__(self, memo=None):
 389             new = self.__class__(deepcopy(self.arg, memo))
 390             new.a = self.a
 391             return new
 392     c = C('argument sketch')
 393     l.append(c)
 394     l2 = copy(l)
 395     print l == l2
 396     print l
 397     print l2
 398     l2 = deepcopy(l)
 399     print l == l2
 400     print l
 401     print l2
 402     l.append({l[1]: l, 'xyz': l[2]})
 403     l3 = copy(l)
 404     import repr
 405     print map(repr.repr, l)
 406     print map(repr.repr, l1)
 407     print map(repr.repr, l2)
 408     print map(repr.repr, l3)
 409     l3 = deepcopy(l)
 410     import repr
 411     print map(repr.repr, l)
 412     print map(repr.repr, l1)
 413     print map(repr.repr, l2)
 414     print map(repr.repr, l3)
 415
 416 if __name__ == '__main__':
 417     _test()