copy — Shallow and deep copy operations¶
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).
Return a shallow copy of x.
Return a deep copy of x.
exception copy. Error ¶
Raised for module specific errors.
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 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:
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() function avoids these problems by:
keeping a memo dictionary of objects already copied during the current copying pass; and
letting user-defined classes override the copying operation or the set of components copied.
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 module.
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 module.
In order for a class to define its own copy implementation, it can define special methods __copy__() and __deepcopy__() . The former is called to implement the shallow copy operation; no additional arguments are passed. The latter is 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.
Discussion of the special methods used to support object state retrieval and restoration.
Six ways to Copy List items in Python
I like to learn cool stuff about python, I have started my Python journey one year ago. Now I am going through the basics of the python to learn more.
I have come across Six ways to copy list items from one list to another in python.
Let's have look at it.
Suppose we want to copy the content of old_list to new_list,
1.Using the Copy() Method: the Copy method of the list object is used to copy only the content inside the list. So the new list will not have the same reference id or memory location. so if we make any changes in the new_list it will not get reflected in the old_ist.
2. Using list() function: List() is built-in function in python. it is also used to create a new list in python. If we pass old_list as an argument inside this function. It copies the content of the old_list and generates a new_list.
The new list will not have same reference id because only content gets copied in this case
Note: Here I have intentionally used copy() as Method and list() as a function to point out the difference. Methods are always called on an object using ‘.’ operator, while function may not. All method is Function but the reverse may not be true.
3. Using List Slicing: List slicing is a way to extract data from a list. So using list slicing if we extract all the content from one list, the new list will have all the content from the old list.
Again this method will only copy content not reference id.
4. Shallow Copy: We can use the copy function of the copy module to get content from one list to another. Again it only copies the content, so the new list will have new Reference id.
5. Deep Copy: We can also use the Deep Copy function of the copy module in the same way as Shallow Copy. Both function works the same for a Normal List having simple content like shown in the example.
There is a difference in the behavior of both the function of the copy module in the case of the Nested List(List inside List).
If you want to know more about the difference between Shallow Copy and Deep Copy feel free to check this link
Suppose we want to copy the content as well as the reference of old_list to new_list,
6. Direct Assigning: If we Assign old_list to the new_list it copies content as well as Reference so changes will be reflected in old_list if it is done in the new_list.
Скопируйте или клонируйте список Python
В этом посте мы обсудим, как скопировать или клонировать список в Python.
Присваивания не копируют списки Python, поскольку они просто создают привязки между исходным и скопированным списками. Это означает, что изменения, сделанные в исходном списке, будут видны в скопированном списке. В этой статье рассматриваются различные способы выполнения общей операции неглубокого копирования в Python.
1. Использование copy() функция
Стандартное решение для возврата неглубокой копии списка — встроенный copy() функция. Эта функция доступна для списков, наборов и словарей.
How to copy a list in Python
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Lists are a commonly used data structure in Python. When you use lists, there may be a situation where you need to copy or clone a list. There are several methods we can use to copy or clone a list.
1. Use copy()
If you need a shallow copy of a list, the built-in copy() function can be used.
This function takes no parameters and returns a shallow copy of the list.
2. Use slicing
List slicing can be used to easily make a copy of a list. This method is called cloning. The original list will remain unchanged.
In this method, slicing is used to copy each element of the original list into the new list.
3. Use a for loop and append()
In this method, a for loop traverses through the elements of the original list and adds them one by one to the copy of the list, through append() . The built-in append() function takes a value as an argument and adds it to the end of a list.
This creates a clone of the original list, so the original list is not changed.