cpython/Lib/copy.py

# 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()