The difference between a=a+2 and a+=2 in Python

1, A=a+2, represents a new object, the new object name is still a, but the point of memory address has changed

>>> a=2>>> ID (a)140406287260016>>> a=a+2>>> a4> >> ID (a)140406287259968

So you can do this for a tuple object (immutable object).

>>> tuple1= >>> ID (tuple1)4521580448>>> tuple1=tuple1+ ( 3,)>>> tuple1 (1, 2, 3)>>> ID (tuple1)4521658880

2. a+=2 for some objects the operation is to represent the original object, the operation of some objects is to generate a new object

Immutable Object Tuple1, after the operation, the memory address has changed, generating a new object
>>> tuple1= >>> type (tuple1)'tuple'>> >> tuple1+= (3,)>>> ID (tuple1)4521658880>>> tuple1+= (4,5)> >> ID (tuple1)4520649072

The list object, variable object, + = operation, append operation, and extend operation are all operated on the original object.

>>> list1=[1,2]>>>ID (list1)4521614656>>> list1+=[3]>>>ID (list1)4521614656>>> List1.append (4)>>>ID (list1)4521614656>>> List1.extend (5) Traceback (most recent): File"<stdin>", Line 1,inch<module>TypeError:'int'Object is  notiterable>>> List1.extend ([5])>>>ID (list1)4521614656>>>

3.

x = [A]  Print "before Func (), global! x ="X"ID (x) =", ID (x)deffunc ():GlobalxPrint "in Func (), local! original x ="X"ID (x) =", ID (x) x= x + [1]      Print "in Func (), local! now x ="X"ID (x) =", ID (x) func ()Print "After func (), global! x ="X"ID (x) =", ID (x) Result: [Python] View plain copybefore func (),Global! x = [1, 2, 3] ID (x) = 47781768inchFunc (), local! Original x = [1, 2, 3] ID (x) = 47781768inchFunc (), local! Now x = [1, 2, 3, 1] ID (x) = 47795720After func (),Global! x = [1, 2, 3, 1] ID (x) = 47795720

GlobalThis ensures that even if my variable x points to the object in the function, the outer x points to the new object.

x = [A]  Print "before Func (), global! x ="X"ID (x) =", ID (x)deffunc (x):Print "in Func (), local! original x ="X"ID (x) =", ID (x) x= x + [1]      Print "in Func (), local! now x ="X"ID (x) =", ID (x) func (x)Print "After func (), global! x ="X"ID (x) =", ID (x) Result: Before Func (),Global! x = [1, 2, 3] ID (x) = 46339976inchFunc (), local! Original x = [1, 2, 3] ID (x) = 46339976inchFunc (), local! Now x = [1, 2, 3, 1] ID (x) = 46390664After func (),Global! x = [1, 2, 3] ID (x) = 46339976

x = x + [1], is a new object, ID (x) = 46390664

Using the ID (x), view the next X + = [1] How does the object change: x= [A]  Print "before Func (), global! x ="X"ID (x) =", ID (x)deffunc (x):Print "in Func (), local! original x ="X"ID (x) =", ID (x) x+ = [1]      Print "in Func (), local! now x ="X"ID (x) =", ID (x) func (x)Print "After func (), global! x ="X"ID (x) =", ID (x) Result: Before Func (),Global! x = [1, 2, 3] ID (x) = 46536584inchFunc (), local! Original x = [1, 2, 3] ID (x) = 46536584inchFunc (), local! Now x = [1, 2, 3, 1] ID (x) = 46536584After func (),Global! x = [1, 2, 3, 1] ID (x) = 46536584
ID (x) as a whole, x + = [1],python directly on the original object

Reference:

1, http://blog.csdn.net/emaste_r/article/details/47395055

The difference between a=a+2 and a+=2 in Python