You can try to do something like this,

In [1]: a = [100] In [2]: b = [100] In [3]: id(a) Out[3]: 79308552L In [4]: id(b) Out[4]: 79342728L In [5]: a += a In [6]: b = b + b In [7]: id(a) Out[7]: 79308552L In [8]: id(b) Out[8]: 79341192L

The memory address allocated to the variable can be obtained through the id() function. Through experiments, it was found that the variable address using+has changed, which is what you said num+=num and num=num+numare not equivalent.
However, when you do the following sexy operations, you will find yourself slapped in the face

In [19]: a = (0,) In [20]: b = (0,) In [21]: id(a) Out[21]: 82230688L In [22]: id(b) Out[22]: 82208920L In [23]: a += a In [24]: b = b + b In [25]: id(a) Out[25]: 79268296L In [26]: id(b) Out[26]: 79328392L

The assigned address seems to keep changing.
The reason is that data structures in Python are divided into mutable and immutable.
For variable types, = and += are obviously different, as shown in the list above:
+ represents a connection operation, += represents appending
For immutable types, = and += are the same operations, such as the tuple above
The essence of variable types and immutable types lies in whether the memory space is variable~

The first thing to notice is the difference

In [26]: def test(num): ...: num = num + num ...: print (num) ...: In [27]: def test1(num): ...: num += num ...: print (num) ...: In [28]: import dis In [29]: dis.dis(test) 2 0 LOAD_FAST 0 (num) 3 LOAD_FAST 0 (num) 6 BINARY_ADD #区别在这儿 7 STORE_FAST 0 (num) 3 10 LOAD_FAST 0 (num) 13 PRINT_ITEM 14 PRINT_NEWLINE 15 LOAD_CONST 0 (None) 18 RETURN_VALUE In [30]: dis.dis(test1) 2 0 LOAD_FAST 0 (num) 3 LOAD_FAST 0 (num) 6 INPLACE_ADD #看这儿 7 STORE_FAST 0 (num) 3 10 LOAD_FAST 0 (num) 13 PRINT_ITEM 14 PRINT_NEWLINE 15 LOAD_CONST 0 (None) 18 RETURN_VALUE

You can see that the methods called are different, they are __add__, __iadd__
The addition operator will calculate a new object to assign to num
The incremental assignment operator modifies the original reference

Reference here: https://stackoverflow.com/que...

Remember that arguments are passed by assignment in Python.

In Python, assignment is used to pass parameters, not reference, so when you pass a to a function, you pass the value of a, not a itself. If you want to change a itself, you need to use return to pass the value back

a = [100] def test(num): num = num + num #这个地方改了一下 return(num) #这个地方再改了一下 print(test(a)) #傳值回來 print(a) a = test(a) print(a)

Result:

[100, 100] [100] [100, 100]

In python, a=a+b means first creating a new object and letting variable a refer to this object. a+=b changes thevalueof the object referenced by a into the value of a+b