Why the output is [1,2,3,4,5,6] not [1,2,3]

Question

a=[1,2,3]
b=a
b+=[4,5,6]
print(a)

Answer 1

Huh. First I didn't see the point of your question but now I understand. In the end you are printing a, but you made the assignment with b.

First point, if you try the code below, it will prove that a and b are two variables pointing to the same object. The id() function shows the memory reference of a value.

a = [1, 2, 3]
b = a
print(id(a) == id(b)) # True

So this means, if you modify b, then a is also automatically modified.

The other part is really tricky and I found the solution in stackoverflow.

https://stackoverflow.com/questions/2347265/why-does-behave-unexpectedly-on-lists

"The general answer is that += tries to call the __iadd__ special method, and if that isn't available it tries to use __add__ instead. So the issue is with the difference between these special methods."

So in your sample code, the assignment b+=[4,5,6] actually does an in-place mutation on b, which is then also reflected in a.

Answer 2

b=a[:]

Answer 3

This is logical! Take a look at your code once more. You created 2 list variables 'a' and 'b' right? a is assigned with [1,2,3] ; variable b is assigned with variable a's, which has automatically set b to a with its value, now you now incremented b with [4,5,6], this will concatenate what value contain in variable a with the new value of b. You have set the values of a and b to the same thing. Print b and see also.

Answer 4

b=a.copy()

Answer 5

Python List Copy Example - How To Clone or Copy List in Python?

https://www.stechies.com/clone-copy-list-python

Answer 6

When we wrote "b=a" then b is become 'a' so,after when you calling' b' but it already converted into 'a' so,then is b+=[4,5,6] is considered as a+=[4,5,6]
that's why the output [1,2,3,4,5,6]

Answer 7

Sister can u help me