mirror of
https://github.com/python/cpython.git
synced 2024-11-27 15:27:06 +01:00
296 lines
8.5 KiB
Python
296 lines
8.5 KiB
Python
"""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.
|
|
"""
|
|
|
|
import types
|
|
import weakref
|
|
from copyreg import dispatch_table
|
|
|
|
class Error(Exception):
|
|
pass
|
|
error = Error # backward compatibility
|
|
|
|
__all__ = ["Error", "copy", "deepcopy", "replace"]
|
|
|
|
def copy(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)
|
|
if copier:
|
|
return copier(x)
|
|
|
|
if issubclass(cls, type):
|
|
# treat it as a regular class:
|
|
return _copy_immutable(x)
|
|
|
|
copier = getattr(cls, "__copy__", None)
|
|
if copier is not None:
|
|
return copier(x)
|
|
|
|
reductor = dispatch_table.get(cls)
|
|
if reductor is not None:
|
|
rv = reductor(x)
|
|
else:
|
|
reductor = getattr(x, "__reduce_ex__", None)
|
|
if reductor is not None:
|
|
rv = reductor(4)
|
|
else:
|
|
reductor = getattr(x, "__reduce__", None)
|
|
if reductor:
|
|
rv = reductor()
|
|
else:
|
|
raise Error("un(shallow)copyable object of type %s" % cls)
|
|
|
|
if isinstance(rv, str):
|
|
return x
|
|
return _reconstruct(x, None, *rv)
|
|
|
|
|
|
_copy_dispatch = d = {}
|
|
|
|
def _copy_immutable(x):
|
|
return x
|
|
for t in (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
|
|
|
|
del d, t
|
|
|
|
def deepcopy(x, memo=None, _nil=[]):
|
|
"""Deep copy operation on arbitrary Python objects.
|
|
|
|
See the module's __doc__ string for more info.
|
|
"""
|
|
|
|
cls = type(x)
|
|
|
|
if cls in _atomic_types:
|
|
return x
|
|
|
|
d = id(x)
|
|
if memo is None:
|
|
memo = {}
|
|
else:
|
|
y = memo.get(d, _nil)
|
|
if y is not _nil:
|
|
return y
|
|
|
|
copier = _deepcopy_dispatch.get(cls)
|
|
if copier is not None:
|
|
y = copier(x, memo)
|
|
else:
|
|
if issubclass(cls, type):
|
|
y = x # atomic copy
|
|
else:
|
|
copier = getattr(x, "__deepcopy__", None)
|
|
if copier is not None:
|
|
y = copier(memo)
|
|
else:
|
|
reductor = dispatch_table.get(cls)
|
|
if reductor:
|
|
rv = reductor(x)
|
|
else:
|
|
reductor = getattr(x, "__reduce_ex__", None)
|
|
if reductor is not None:
|
|
rv = reductor(4)
|
|
else:
|
|
reductor = getattr(x, "__reduce__", None)
|
|
if reductor:
|
|
rv = reductor()
|
|
else:
|
|
raise Error(
|
|
"un(deep)copyable object of type %s" % cls)
|
|
if isinstance(rv, str):
|
|
y = x
|
|
else:
|
|
y = _reconstruct(x, memo, *rv)
|
|
|
|
# If is its own copy, don't memoize.
|
|
if y is not x:
|
|
memo[d] = y
|
|
_keep_alive(x, memo) # Make sure x lives at least as long as d
|
|
return y
|
|
|
|
_atomic_types = {types.NoneType, types.EllipsisType, types.NotImplementedType,
|
|
int, float, bool, complex, bytes, str, types.CodeType, type, range,
|
|
types.BuiltinFunctionType, types.FunctionType, weakref.ref, property}
|
|
|
|
_deepcopy_dispatch = d = {}
|
|
|
|
|
|
def _deepcopy_list(x, memo, deepcopy=deepcopy):
|
|
y = []
|
|
memo[id(x)] = y
|
|
append = y.append
|
|
for a in x:
|
|
append(deepcopy(a, memo))
|
|
return y
|
|
d[list] = _deepcopy_list
|
|
|
|
def _deepcopy_tuple(x, memo, deepcopy=deepcopy):
|
|
y = [deepcopy(a, memo) for a in x]
|
|
# 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:
|
|
return memo[id(x)]
|
|
except KeyError:
|
|
pass
|
|
for k, j in zip(x, y):
|
|
if k is not j:
|
|
y = tuple(y)
|
|
break
|
|
else:
|
|
y = x
|
|
return y
|
|
d[tuple] = _deepcopy_tuple
|
|
|
|
def _deepcopy_dict(x, memo, deepcopy=deepcopy):
|
|
y = {}
|
|
memo[id(x)] = y
|
|
for key, value in x.items():
|
|
y[deepcopy(key, memo)] = deepcopy(value, memo)
|
|
return y
|
|
d[dict] = _deepcopy_dict
|
|
|
|
def _deepcopy_method(x, memo): # Copy instance methods
|
|
return type(x)(x.__func__, deepcopy(x.__self__, memo))
|
|
d[types.MethodType] = _deepcopy_method
|
|
|
|
del d
|
|
|
|
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)
|
|
except KeyError:
|
|
# 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 = memo is not None
|
|
if deep and args:
|
|
args = (deepcopy(arg, memo) for arg in args)
|
|
y = func(*args)
|
|
if deep:
|
|
memo[id(x)] = y
|
|
|
|
if state is not None:
|
|
if deep:
|
|
state = deepcopy(state, memo)
|
|
if hasattr(y, '__setstate__'):
|
|
y.__setstate__(state)
|
|
else:
|
|
if isinstance(state, tuple) and len(state) == 2:
|
|
state, slotstate = state
|
|
else:
|
|
slotstate = None
|
|
if state is not None:
|
|
y.__dict__.update(state)
|
|
if slotstate is not None:
|
|
for key, value in slotstate.items():
|
|
setattr(y, key, value)
|
|
|
|
if listiter is not None:
|
|
if deep:
|
|
for item in listiter:
|
|
item = deepcopy(item, memo)
|
|
y.append(item)
|
|
else:
|
|
for item in listiter:
|
|
y.append(item)
|
|
if dictiter is not None:
|
|
if deep:
|
|
for key, value in dictiter:
|
|
key = deepcopy(key, memo)
|
|
value = deepcopy(value, memo)
|
|
y[key] = value
|
|
else:
|
|
for key, value in dictiter:
|
|
y[key] = value
|
|
return y
|
|
|
|
del types, weakref
|
|
|
|
|
|
def replace(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)
|
|
if func is None:
|
|
raise TypeError(f"replace() does not support {cls.__name__} objects")
|
|
return func(obj, **changes)
|