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# Generic (shallow and deep) copying operations
# =============================================
#
# The difference between shallow and deep copying is only relevant for
# compound objects (objects that contain other objects, like lists or class
# instances).
#
# - A shallow copy constructs a new compound object and then (to the extent
# possible) inserts *the same objects* into in that the original contains.
#
# - A deep copy constructs a new compound object and then, recursively,
# inserts *copies* into it of the objects found in the original.
#
# Two problems often exist with deep copy operations that don't exist with
# shallow copy operations:
#
# (a) recursive objects (compound objects that, directly or indirectly,
# contain a reference to themselves) may cause a recursive loop
#
# (b) because deep copy copies *everything* it may copy too much, e.g.
# administrative data structures that should be shared even between copies
#
# Python's deep copy operation avoids these problems by:
#
# (a) keeping a table of objects already copied during the current copying pass
#
# (b) letting user-defined classes override the copying operation or the set
# of components copied
#
# This version does not copy types like module, class, function, method,
# nor stack trace, stack frame, nor file, socket, window, nor array,
# nor any similar types.
import types
Error = 'copy.Error'
def copy(x):
try:
copierfunction = _copy_dispatch[type(x)]
except KeyError:
try:
copier = x.__copy__
except AttributeError:
raise Error, "un(shallow)copyable object of type %s" % type(x)
y = copier()
else:
y = copierfunction(x)
return y
_copy_dispatch = d = {}
def _copy_atomic(x):
return x
d[types.NoneType] = _copy_atomic
d[types.IntType] = _copy_atomic
d[types.LongType] = _copy_atomic
d[types.FloatType] = _copy_atomic
d[types.StringType] = _copy_atomic
d[types.CodeType] = _copy_atomic
d[types.TypeType] = _copy_atomic
d[types.XRangeType] = _copy_atomic
def _copy_list(x):
return x[:]
d[types.ListType] = _copy_list
def _copy_tuple(x):
return x[:]
d[types.TupleType] = _copy_tuple
def _copy_dict(x):
y = {}
for key in x.keys():
y[key] = x[key]
return y
d[types.DictionaryType] = _copy_dict
def _copy_inst(x):
if hasattr(x, '__copy__'):
return x.__copy__()
if hasattr(x, '__getinitargs__'):
args = x.__getinitargs__()
else:
args = ()
y = apply(x.__class__, args)
if hasattr(x, '__getstate__'):
state = x.__getstate__()
else:
state = x.__dict__
if y.hasattr('__setstate__'):
y.__setstate__(state)
else:
for key in state.keys():
setattr(y, key, state[key])
return y
d[types.InstanceType] = _copy_inst
del d
def deepcopy(x, memo = None):
if memo is None:
memo = {}
d = id(x)
if memo.has_key(d):
return memo[d]
try:
copierfunction = _deepcopy_dispatch[type(x)]
except KeyError:
try:
copier = x.__deepcopy__
except AttributeError:
raise Error, "un-deep-copyable object of type %s" % type(x)
y = copier(memo)
else:
y = copierfunction(x, memo)
memo[d] = y
return y
_deepcopy_dispatch = d = {}
def _deepcopy_atomic(x, memo):
return x
d[types.NoneType] = _deepcopy_atomic
d[types.IntType] = _deepcopy_atomic
d[types.LongType] = _deepcopy_atomic
d[types.FloatType] = _deepcopy_atomic
d[types.StringType] = _deepcopy_atomic
d[types.CodeType] = _deepcopy_atomic
d[types.TypeType] = _deepcopy_atomic
d[types.XRangeType] = _deepcopy_atomic
def _deepcopy_list(x, memo):
y = []
memo[id(x)] = y
for a in x:
y.append(deepcopy(a, memo))
return y
d[types.ListType] = _deepcopy_list
def _deepcopy_tuple(x, memo):
y = []
for a in x:
y.append(deepcopy(a, memo))
d = id(x)
try:
return memo[d]
except KeyError:
pass
for i in range(len(x)):
if x[i] is not y[i]:
return tuple(y)
return x
d[types.TupleType] = _deepcopy_tuple
def _deepcopy_dict(x, memo):
y = {}
memo[id(x)] = y
for key in x.keys():
y[deepcopy(key, memo)] = deepcopy(x[key], memo)
return y
d[types.DictionaryType] = _deepcopy_dict
def _deepcopy_inst(x, memo):
if hasattr(x, '__deepcopy__'):
return x.__deepcopy__()
if hasattr(x, '__getinitargs__'):
args = x.__getinitargs__()
args = deepcopy(args, memo)
else:
args = ()
y = apply(x.__class__, args)
memo[id(x)] = y
if hasattr(x, '__getstate__'):
state = x.__getstate__()
else:
state = x.__dict__
state = deepcopy(state, memo)
if y.hasattr('__setstate__'):
y.__setstate__(state)
else:
for key in state.keys():
setattr(y, key, state[key])
return y
d[types.InstanceType] = _deepcopy_inst
del d
del types
def _test():
l = [None, 1, 2L, 3.14, 'xyzzy', (1, 2L), [3.14, 'abc'], {'abc': 'ABC'}, (), [], {}]
l1 = copy(l)
print l1==l
l1 = map(copy, l)
print l1==l
l1 = deepcopy(l)
print l1==l
class C:
def __init__(self, arg=None):
self.a = 1
self.arg = arg
self.fp = open('copy.py')
self.fp.close()
def __getstate__(self):
return {'a': self.a, 'arg': self.arg}
def __setstate__(self, state):
for key in state.keys():
setattr(self, key, state[key])
def __deepcopy__(self, memo = None):
new = self.__class__(deepcopy(self.arg, memo))
new.a = self.a
return new
c = C('argument sketch')
l.append(c)
l2 = copy(l)
print l == l2
print l
print l2
l2 = deepcopy(l)
print l == l2
print l
print l2
l.append({l[1]: l, 'xyz': l[2]})
l3 = copy(l)
import repr
print map(repr.repr, l)
print map(repr.repr, l1)
print map(repr.repr, l2)
print map(repr.repr, l3)
l3 = deepcopy(l)
import repr
print map(repr.repr, l)
print map(repr.repr, l1)
print map(repr.repr, l2)
print map(repr.repr, l3)
if __name__ == '__main__':
_test()
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