Python's value types and reference types and the difference between value passing and reference passing

Value type:

Contains: string, tuple, value, itself is not allowed to be modified

Reference type:

Contains: list, dictionary, itself is allowed Modify

a = 2

b = a

a = 3

Modify the value of the value type, just let it point to a The new memory address will not change the value of variable b

lista = [1,2]

listb = lista

lista[0 ] = 3

Modify the value of the reference type. Because the address of listb is consistent with lista, it will also be modified

Generally just to copy the value, you can use the sharding operation

listb = lista[:]

Value passing only passes the value
Reference passing passes the memory address. After modification, the value stored corresponding to the memory address will be changed.
It is clearest to use an array as an example. For example, if we define an array a[]={1,2};
then a[0]=1,a[1]=2.
If we pass the element value in the array a as a parameter, it is actually just a value transfer and has no effect on the array itself.
If we pass the pointer of the array a as a parameter, then the processing function can Directly modify the value in array a.

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