copy.py

"""Generic (shallow and deep) copying operations.

Interface summary:

 import copy

 x = copy.copy(y) # make a shallow copy of y
 x = copy.deepcopy(y) # make a deep copy of y
 x = copy.replace(y, a=1, b=2) # new object with fields replaced, as defined by `__replace__`

For module specific errors, copy.Error is raised.

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 it 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 any
similar types.

Classes can use the same interfaces to control copying that they use
to control pickling: they can define methods called __getinitargs__(),
__getstate__() and __setstate__(). See the documentation for module
"pickle" for information on these methods.
"""

importtypes
importweakref
fromcopyregimportdispatch_table

classError(Exception):
pass
error=Error# backward compatibility

__all__= ["Error", "copy", "deepcopy", "replace"]

defcopy(x):
"""Shallow copy operation on arbitrary Python objects.

 See the module's __doc__ string for more info.
 """

cls=type(x)

copier=_copy_dispatch.get(cls)
ifcopier:
returncopier(x)

ifissubclass(cls, type):
# treat it as a regular class:
return_copy_immutable(x)

copier=getattr(cls, "__copy__", None)
ifcopierisnotNone:
returncopier(x)

reductor=dispatch_table.get(cls)
ifreductorisnotNone:
rv=reductor(x)
else:
reductor=getattr(x, "__reduce_ex__", None)
ifreductorisnotNone:
rv=reductor(4)
else:
reductor=getattr(x, "__reduce__", None)
ifreductor:
rv=reductor()
else:
raiseError("un(shallow)copyable object of type %s"%cls)

ifisinstance(rv, str):
returnx
return_reconstruct(x, None, *rv)


_copy_dispatch=d= {}

def_copy_immutable(x):
returnx
fortin (types.NoneType, int, float, bool, complex, str, tuple,
bytes, frozenset, type, range, slice, property,
types.BuiltinFunctionType, types.EllipsisType,
types.NotImplementedType, types.FunctionType, types.CodeType,
weakref.ref):
d[t] =_copy_immutable

d[list] =list.copy
d[dict] =dict.copy
d[set] =set.copy
d[bytearray] =bytearray.copy

deld, t

defdeepcopy(x, memo=None, _nil=[]):
"""Deep copy operation on arbitrary Python objects.

 See the module's __doc__ string for more info.
 """

d=id(x)
ifmemoisNone:
memo= {}
else:
y=memo.get(d, _nil)
ifyisnot_nil:
returny

cls=type(x)

copier=_deepcopy_dispatch.get(cls)
ifcopierisnotNone:
y=copier(x, memo)
else:
ifissubclass(cls, type):
y=_deepcopy_atomic(x, memo)
else:
copier=getattr(x, "__deepcopy__", None)
ifcopierisnotNone:
y=copier(memo)
else:
reductor=dispatch_table.get(cls)
ifreductor:
rv=reductor(x)
else:
reductor=getattr(x, "__reduce_ex__", None)
ifreductorisnotNone:
rv=reductor(4)
else:
reductor=getattr(x, "__reduce__", None)
ifreductor:
rv=reductor()
else:
raiseError(
"un(deep)copyable object of type %s"%cls)
ifisinstance(rv, str):
y=x
else:
y=_reconstruct(x, memo, *rv)

# If is its own copy, don't memoize.
ifyisnotx:
memo[d] =y
_keep_alive(x, memo) # Make sure x lives at least as long as d
returny

_deepcopy_dispatch=d= {}

def_deepcopy_atomic(x, memo):
returnx
d[types.NoneType] =_deepcopy_atomic
d[types.EllipsisType] =_deepcopy_atomic
d[types.NotImplementedType] =_deepcopy_atomic
d[int] =_deepcopy_atomic
d[float] =_deepcopy_atomic
d[bool] =_deepcopy_atomic
d[complex] =_deepcopy_atomic
d[bytes] =_deepcopy_atomic
d[str] =_deepcopy_atomic
d[types.CodeType] =_deepcopy_atomic
d[type] =_deepcopy_atomic
d[range] =_deepcopy_atomic
d[types.BuiltinFunctionType] =_deepcopy_atomic
d[types.FunctionType] =_deepcopy_atomic
d[weakref.ref] =_deepcopy_atomic
d[property] =_deepcopy_atomic

def_deepcopy_list(x, memo, deepcopy=deepcopy):
y= []
memo[id(x)] =y
append=y.append
forainx:
append(deepcopy(a, memo))
returny
d[list] =_deepcopy_list

def_deepcopy_tuple(x, memo, deepcopy=deepcopy):
y= [deepcopy(a, memo) forainx]
# We're not going to put the tuple in the memo, but it's still important we
# check for it, in case the tuple contains recursive mutable structures.
try:
returnmemo[id(x)]
exceptKeyError:
pass
fork, jinzip(x, y):
ifkisnotj:
y=tuple(y)
break
else:
y=x
returny
d[tuple] =_deepcopy_tuple

def_deepcopy_dict(x, memo, deepcopy=deepcopy):
y= {}
memo[id(x)] =y
forkey, valueinx.items():
y[deepcopy(key, memo)] =deepcopy(value, memo)
returny
d[dict] =_deepcopy_dict

def_deepcopy_method(x, memo): # Copy instance methods
returntype(x)(x.__func__, deepcopy(x.__self__, memo))
d[types.MethodType] =_deepcopy_method

deld

def_keep_alive(x, memo):
"""Keeps a reference to the object x in the memo.

 Because we remember objects by their id, we have
 to assure that possibly temporary objects are kept
 alive by referencing them.
 We store a reference at the id of the memo, which should
 normally not be used unless someone tries to deepcopy
 the memo itself...
 """
try:
memo[id(memo)].append(x)
exceptKeyError:
# aha, this is the first one :-)
memo[id(memo)]=[x]

def_reconstruct(x, memo, func, args,
state=None, listiter=None, dictiter=None,
*, deepcopy=deepcopy):
deep=memoisnotNone
ifdeepandargs:
args= (deepcopy(arg, memo) forarginargs)
y=func(*args)
ifdeep:
memo[id(x)] =y

ifstateisnotNone:
ifdeep:
state=deepcopy(state, memo)
ifhasattr(y, '__setstate__'):
y.__setstate__(state)
else:
ifisinstance(state, tuple) andlen(state) ==2:
state, slotstate=state
else:
slotstate=None
ifstateisnotNone:
y.__dict__.update(state)
ifslotstateisnotNone:
forkey, valueinslotstate.items():
setattr(y, key, value)

iflistiterisnotNone:
ifdeep:
foriteminlistiter:
item=deepcopy(item, memo)
y.append(item)
else:
foriteminlistiter:
y.append(item)
ifdictiterisnotNone:
ifdeep:
forkey, valueindictiter:
key=deepcopy(key, memo)
value=deepcopy(value, memo)
y[key] =value
else:
forkey, valueindictiter:
y[key] =value
returny

deltypes, weakref


defreplace(obj, /, **changes):
"""Return a new object replacing specified fields with new values.

 This is especially useful for immutable objects, like named tuples or
 frozen dataclasses.
 """
cls=obj.__class__
func=getattr(cls, '__replace__', None)
iffuncisNone:
raiseTypeError(f"replace() does not support {cls.__name__} objects")
returnfunc(obj, **changes)