copy
— 浅拷贝和深拷贝操作
¶
源代码：
Lib/copy.py
Assignment statements in Python do not copy objects, they create bindings between a target and an object. For collections that are mutable or contain mutable items, a copy is sometimes needed so one can change one copy without changing the other. This module provides generic shallow and deep copy operations (explained below).
接口摘要：
-
copy.
copy
(
obj
)
¶
-
返回浅拷贝为
obj
.
-
copy.
deepcopy
(
obj
[
,
memo
]
)
¶
-
返回深拷贝的
obj
.
-
copy.
replace
(
obj
,
/
,
**
changes
)
¶
-
创建相同类型的新对象如
obj
, replacing fields with values from
changes
.
3.13 版添加。
-
exception
copy.
Error
¶
-
为模块特定错误而引发。
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
references
into it to the objects found in the original.
-
A
深拷贝
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:
-
Recursive objects (compound objects that, directly or indirectly, contain a reference to themselves) may cause a recursive loop.
-
Because deep copy copies everything it may copy too much, such as data which is intended to be shared between copies.
The
deepcopy()
函数避免了这些问题通过：
This module does not copy types like module, method, stack trace, stack frame, file, socket, window, or any similar types. It does “copy” functions and classes (shallow and deeply), by returning the original object unchanged; this is compatible with the way these are treated by the
pickle
模块。
Shallow copies of dictionaries can be made using
dict.copy()
, and of lists by assigning a slice of the entire list, for example,
copied_list = original_list[:]
.
Classes can use the same interfaces to control copying that they use to control pickling. See the description of module
pickle
for information on these methods. In fact, the
copy
module uses the registered pickle functions from the
copyreg
模块。
In order for a class to define its own copy implementation, it can define special methods
__copy__()
and
__deepcopy__()
.
-
对象。
__copy__
(
self
)
¶
-
Called to implement the shallow copy operation; no additional arguments are passed.
-
对象。
__deepcopy__
(
self
,
memo
)
¶
-
Called to implement the deep copy operation; it is passed one argument, the
memo
dictionary. If the
__deepcopy__
implementation needs to make a deep copy of a component, it should call the
deepcopy()
function with the component as first argument and the
memo
dictionary as second argument. The
memo
dictionary should be treated as an opaque object.
函数
copy.replace()
is more limited than
copy()
and
deepcopy()
, and only supports named tuples created by
namedtuple()
,
dataclasses
, and other classes which define method
__replace__()
.
-
对象。
__replace__
(
self
,
/
,
**
changes
)
¶
-
This method should create a new object of the same type, replacing fields with values from
changes
.
另请参阅
-
模块
pickle
-
Discussion of the special methods used to support object state retrieval and restoration.
