|
| 1 | +# Generic (shallow and deep) copying operations |
| 2 | +# ============================================= |
| 3 | +# |
| 4 | +# The difference between shallow and deep copying is only relevant for |
| 5 | +# compound objects (objects that contain other objects, like lists or class |
| 6 | +# instances). |
| 7 | +# |
| 8 | +# - A shallow copy constructs a new compound object and then (to the extent |
| 9 | +# possible) inserts *the same objects* into in that the original contains. |
| 10 | +# |
| 11 | +# - A deep copy constructs a new compound object and then, recursively, |
| 12 | +# inserts *copies* into it of the objects found in the original. |
| 13 | +# |
| 14 | +# Two problems often exist with deep copy operations that don't exist with |
| 15 | +# shallow copy operations: |
| 16 | +# |
| 17 | +# (a) recursive objects (compound objects that, directly or indirectly, |
| 18 | +# contain a reference to themselves) may cause a recursive loop |
| 19 | +# |
| 20 | +# (b) because deep copy copies *everything* it may copy too much, e.g. |
| 21 | +# administrative data structures that should be shared even between copies |
| 22 | +# |
| 23 | +# Python's deep copy operation avoids these problems by: |
| 24 | +# |
| 25 | +# (a) keeping a table of objects already copied during the current copying pass |
| 26 | +# |
| 27 | +# (b) letting user-defined classes override the copying operation or the set |
| 28 | +# of components copied |
| 29 | +# |
| 30 | +# This version does not copy types like module, class, function, method, |
| 31 | +# nor stack trace, stack frame, nor file, socket, window, nor array, |
| 32 | +# nor any similar types. |
| 33 | + |
| 34 | + |
| 35 | +import types |
| 36 | + |
| 37 | +Error = 'copy.Error' |
| 38 | + |
| 39 | +def copy(x): |
| 40 | + try: |
| 41 | + copierfunction = _copy_dispatch[type(x)] |
| 42 | + except KeyError: |
| 43 | + try: |
| 44 | + copier = x.__copy__ |
| 45 | + except AttributeError: |
| 46 | + raise Error, "un(shallow)copyable object of type %s" % type(x) |
| 47 | + y = copier() |
| 48 | + else: |
| 49 | + y = copierfunction(x) |
| 50 | + return y |
| 51 | + |
| 52 | +_copy_dispatch = d = {} |
| 53 | + |
| 54 | +def _copy_atomic(x): |
| 55 | + return x |
| 56 | +d[types.NoneType] = _copy_atomic |
| 57 | +d[types.IntType] = _copy_atomic |
| 58 | +d[types.LongType] = _copy_atomic |
| 59 | +d[types.FloatType] = _copy_atomic |
| 60 | +d[types.StringType] = _copy_atomic |
| 61 | +d[types.CodeType] = _copy_atomic |
| 62 | +d[types.TypeType] = _copy_atomic |
| 63 | +d[types.XRangeType] = _copy_atomic |
| 64 | + |
| 65 | +def _copy_list(x): |
| 66 | + return x[:] |
| 67 | +d[types.ListType] = _copy_list |
| 68 | + |
| 69 | +def _copy_tuple(x): |
| 70 | + return x[:] |
| 71 | +d[types.TupleType] = _copy_tuple |
| 72 | + |
| 73 | +def _copy_dict(x): |
| 74 | + y = {} |
| 75 | + for key in x.keys(): |
| 76 | + y[key] = x[key] |
| 77 | + return y |
| 78 | +d[types.DictionaryType] = _copy_dict |
| 79 | + |
| 80 | +def _copy_inst(x): |
| 81 | + if hasattr(x, '__copy__'): |
| 82 | + return x.__copy__() |
| 83 | + if hasattr(x, '__getinitargs__'): |
| 84 | + args = x.__getinitargs__() |
| 85 | + else: |
| 86 | + args = () |
| 87 | + y = apply(x.__class__, args) |
| 88 | + if hasattr(x, '__getstate__'): |
| 89 | + state = x.__getstate__() |
| 90 | + else: |
| 91 | + state = x.__dict__ |
| 92 | + if y.hasattr('__setstate__'): |
| 93 | + y.__setstate__(state) |
| 94 | + else: |
| 95 | + for key in state.keys(): |
| 96 | + setattr(y, key, state[key]) |
| 97 | + return y |
| 98 | +d[types.InstanceType] = _copy_inst |
| 99 | + |
| 100 | +del d |
| 101 | + |
| 102 | +def deepcopy(x, memo = None): |
| 103 | + if memo is None: |
| 104 | + memo = {} |
| 105 | + d = id(x) |
| 106 | + if memo.has_key(d): |
| 107 | + return memo[d] |
| 108 | + try: |
| 109 | + copierfunction = _deepcopy_dispatch[type(x)] |
| 110 | + except KeyError: |
| 111 | + try: |
| 112 | + copier = x.__deepcopy__ |
| 113 | + except AttributeError: |
| 114 | + raise Error, "un-deep-copyable object of type %s" % type(x) |
| 115 | + y = copier(memo) |
| 116 | + else: |
| 117 | + y = copierfunction(x, memo) |
| 118 | + memo[d] = y |
| 119 | + return y |
| 120 | + |
| 121 | +_deepcopy_dispatch = d = {} |
| 122 | + |
| 123 | +def _deepcopy_atomic(x, memo): |
| 124 | + return x |
| 125 | +d[types.NoneType] = _deepcopy_atomic |
| 126 | +d[types.IntType] = _deepcopy_atomic |
| 127 | +d[types.LongType] = _deepcopy_atomic |
| 128 | +d[types.FloatType] = _deepcopy_atomic |
| 129 | +d[types.StringType] = _deepcopy_atomic |
| 130 | +d[types.CodeType] = _deepcopy_atomic |
| 131 | +d[types.TypeType] = _deepcopy_atomic |
| 132 | +d[types.XRangeType] = _deepcopy_atomic |
| 133 | + |
| 134 | +def _deepcopy_list(x, memo): |
| 135 | + y = [] |
| 136 | + memo[id(x)] = y |
| 137 | + for a in x: |
| 138 | + y.append(deepcopy(a, memo)) |
| 139 | + return y |
| 140 | +d[types.ListType] = _deepcopy_list |
| 141 | + |
| 142 | +def _deepcopy_tuple(x, memo): |
| 143 | + y = [] |
| 144 | + for a in x: |
| 145 | + y.append(deepcopy(a, memo)) |
| 146 | + d = id(x) |
| 147 | + try: |
| 148 | + return memo[d] |
| 149 | + except KeyError: |
| 150 | + pass |
| 151 | + for i in range(len(x)): |
| 152 | + if x[i] is not y[i]: |
| 153 | + return tuple(y) |
| 154 | + return x |
| 155 | +d[types.TupleType] = _deepcopy_tuple |
| 156 | + |
| 157 | +def _deepcopy_dict(x, memo): |
| 158 | + y = {} |
| 159 | + memo[id(x)] = y |
| 160 | + for key in x.keys(): |
| 161 | + y[deepcopy(key, memo)] = deepcopy(x[key], memo) |
| 162 | + return y |
| 163 | +d[types.DictionaryType] = _deepcopy_dict |
| 164 | + |
| 165 | +def _deepcopy_inst(x, memo): |
| 166 | + if hasattr(x, '__deepcopy__'): |
| 167 | + return x.__deepcopy__() |
| 168 | + if hasattr(x, '__getinitargs__'): |
| 169 | + args = x.__getinitargs__() |
| 170 | + args = deepcopy(args, memo) |
| 171 | + else: |
| 172 | + args = () |
| 173 | + y = apply(x.__class__, args) |
| 174 | + memo[id(x)] = y |
| 175 | + if hasattr(x, '__getstate__'): |
| 176 | + state = x.__getstate__() |
| 177 | + else: |
| 178 | + state = x.__dict__ |
| 179 | + state = deepcopy(state, memo) |
| 180 | + if y.hasattr('__setstate__'): |
| 181 | + y.__setstate__(state) |
| 182 | + else: |
| 183 | + for key in state.keys(): |
| 184 | + setattr(y, key, state[key]) |
| 185 | + return y |
| 186 | +d[types.InstanceType] = _deepcopy_inst |
| 187 | + |
| 188 | +del d |
| 189 | + |
| 190 | +del types |
| 191 | + |
| 192 | +def _test(): |
| 193 | + l = [None, 1, 2L, 3.14, 'xyzzy', (1, 2L), [3.14, 'abc'], {'abc': 'ABC'}, (), [], {}] |
| 194 | + l1 = copy(l) |
| 195 | + print l1==l |
| 196 | + l1 = map(copy, l) |
| 197 | + print l1==l |
| 198 | + l1 = deepcopy(l) |
| 199 | + print l1==l |
| 200 | + class C: |
| 201 | + def __init__(self, arg=None): |
| 202 | + self.a = 1 |
| 203 | + self.arg = arg |
| 204 | + self.fp = open('copy.py') |
| 205 | + self.fp.close() |
| 206 | + def __getstate__(self): |
| 207 | + return {'a': self.a, 'arg': self.arg} |
| 208 | + def __setstate__(self, state): |
| 209 | + for key in state.keys(): |
| 210 | + setattr(self, key, state[key]) |
| 211 | + def __deepcopy__(self, memo = None): |
| 212 | + new = self.__class__(deepcopy(self.arg, memo)) |
| 213 | + new.a = self.a |
| 214 | + return new |
| 215 | + c = C('argument sketch') |
| 216 | + l.append(c) |
| 217 | + l2 = copy(l) |
| 218 | + print l == l2 |
| 219 | + print l |
| 220 | + print l2 |
| 221 | + l2 = deepcopy(l) |
| 222 | + print l == l2 |
| 223 | + print l |
| 224 | + print l2 |
| 225 | + l.append({l[1]: l, 'xyz': l[2]}) |
| 226 | + l3 = copy(l) |
| 227 | + import repr |
| 228 | + print map(repr.repr, l) |
| 229 | + print map(repr.repr, l1) |
| 230 | + print map(repr.repr, l2) |
| 231 | + print map(repr.repr, l3) |
| 232 | + l3 = deepcopy(l) |
| 233 | + import repr |
| 234 | + print map(repr.repr, l) |
| 235 | + print map(repr.repr, l1) |
| 236 | + print map(repr.repr, l2) |
| 237 | + print map(repr.repr, l3) |
| 238 | + |
| 239 | +if __name__ == '__main__': |
| 240 | + _test() |
0 commit comments