What is the output of the following code? #PYTHON

Question

What is the output of the following code?
L,D=[],[]
for x in range(4):
D.append(x)
L.append(D)
print(L[0])

What I think the answer should be...
1st if all L and D are both empty lists.
Then we in the next line we say for x in range(4) so the range will be [0,1,2,3] .
Now, with the value x=0 the value 0 should be added to the list and now the D is [0].
And similarly in next step we add D to List L which should make L=[[0]]
So when the for loop runs 2nd time with x=1
D becomes [0,1]
And L becomes [[0],[0,1]]
And like this when the for loop runs for the last time with x= 3
D will become [0,1,2,3]
And L will become [[0],[0,1],[0,1,2],[0,1,2,3]]
So at last when we give command print(L[0])
Shouldn't it print [0]????
But the answer was [0,1,2,3]
I think this would be the answer if the code looks like this
L,D=[],[]
for x in range(4):
D.append(x)
L.append(D)
print(L[0])
In this L.append(D) is out of for loop so when the for loop is done with D=[0,1,2,3].. then L.append(D) will take the value[ [0,1,2,3]]

Answer 1

Rohit
Well, what happens if you add some more code to alter a after it was added to b? I believe b's content also changes.

Try adding

a.append(42)
print(b)

https://code.sololearn.com/cm1r361gZVQm/?ref=app

Answer 2

~ swim ~ ChrA thanks guys

Answer 3

Hi.

If you take the print command inside the loop an observer the content of complete L and complete D it appears that the insertion of D in L is not actually putting copies of D in L but reference (I think I remember that from the tutorial as well)
So in fact the references in L always show the current contents of D.

Hope that helps. Cheers. C

Answer 4

ChrA

Well if I understand your answer correct you are saying that L is just a reference to D. But doesn't append add an element to the list even if the element is list it self.

I tried this:
a=[1,2]
b=[2,3]
b.append(a)
print(b)

Output was [1,2,[2,3]]

So I think I'm not able to understand what you are trying to say.. Sorry and thanks for you efforts and time... If possible please explain again.. Thank you