Example analysis of references and replication usages in Python

The examples in this article describe references and replication usage in Python. Share to everyone for your reference. The specific analysis is as follows:

In Python, any immutable object is a value, and a Mutable object is a reference.

Immutable objects (such as integers, strings) are actually copied, whether they are passing arguments to a function or any form of object copying, and mutable objects simply copy a reference to them, that is, there is only one object in memory, and two copies are referenced.

A=b Such an assignment creates a reference to B, and for immutable objects such as numbers and strings, this assignment actually creates a copy of B

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>>> a= ' Hello ' >>> b=a >>> ID (a) 29326432 >>> ID (b) 29326432 >>> B is a True & gt;>> a=1000 >>> B ' Hello '

For mutable objects, such as dictionaries and lists, A and B refer to the same object, and modifying any one of these variables affects the other.

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>>> a=[1,2,3,4] >>> b=a >>> ID (a) 29280896 >>> ID (b) 29280896 >>> b[3]= ' CCCC CCCCC ' >>> A [1, 2, 3, ' CCCCCCCCC '] >>>

A container object such as a list and a dictionary can use two assignment operations: shallow copy and deep copy. Shallow copy creates a new object, but it contains a reference to the items contained in the original object.

For example, the following shallow copy:

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>>> a=[1,2,3,4,[9,0]] >>> b=a >>> a=[1,2,3,4,[9,0]] >>> b=list (a) >>> B is a False >>> b[0]=1000 >>> b [1000, 2, 3, 4, [9, 0]] #注意, b modified b[0] After, to a no effect >>> a [1, 2, 3, 4, [9, 0]] >>> b[4][1]= ' CCCC ' #注意, b modified b[4][1] After, to a has influence >>> b [1000, 2, 3, 4, [9, ' CCCC ']] >>> a [1, 2 , 3, 4, [9, ' CCCC ']]

Deep copy creates a new object and recursively replicates all the objects it contains, no built-in objects can create deep copy, and can be done using the copy.deepcopy () function.

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>>> import copy >>> a=[1,2,3,[4,5]] >>> b=copy.deepcopy (a) >>> ID (b) 29582240 >& Gt;> ID (a) 29581840 >>> A is b False >>> b[0]=1000 >>> b [1000, 2, 3, [4, 5]] #注意修改了b [0] after a No impact >>> A [1, 2, 3, [4, 5]] >>> b[3][1]= ' gggg ' >>> b [1000, 2, 3, [4, ' GGGG ']] after #修改了 b[3][1] A also has no effect, this is the difference with the shallow copy >>> a [1, 2, 3, [4, 5]]

I hope this article will help you with your Python programming.