Insert an array in an array using loop

Question

I write the following code to create an array like [[1,2,3],[2,2,3],[3,2,3]],

def f(X):
    X[0]=X[0]+1
    return X
L=[]
X=[1,2,3]
for i in range(0,3):
    L=L+[X]
    X=f(X)
print(L)

But it is printing [[4, 2, 3], [4, 2, 3], [4, 2, 3]]. Why it is happening and how to solve this using the function 'f'?

Thanks

Questions seeking debugging help ("why isn't this code working?") must include the desired behavior, a specific problem or error and the shortest code necessary to reproduce it in the question itself. Questions without a clear problem statement are not useful to other readers. See: [How to create a Minimal, Complete, and Verifiable example](http://stackoverflow.com/help/mcve). — barak manos, Nov 28 '16 at 15:06
What's happening is pretty obvious, to solve just use a copy of X in f(). — polku, Nov 28 '16 at 15:07
You pass reference to same object all three times. Because of that, when You change list, it will change everywhere You used this reference. — Fejs, Nov 28 '16 at 15:10
It can be solved in various ways, but I don't see any point in yours. — barak manos, Nov 28 '16 at 15:16
In another program I wrote a function that generates lists and these lists can not be simply generated like those in my question and I want to create a list of that lists. That's why I want help. @barak manos — Perth, Nov 28 '16 at 15:21
Well, post the actual purpose, so we can relate to that. You can't seriously expect us to "twist" the answer so that it will be suitable for some other unknown purpose of yours. — barak manos, Nov 28 '16 at 15:26
Is this a duplicate of http://stackoverflow.com/questions/2612802/how-to-clone-or-copy-a-list? — doctorlove, Nov 28 '16 at 16:11

score 0 · Accepted Answer · answered Nov 28 '16 at 15:17

0

If you have to use your function f, then try as follows:

l = []
x = [1, 2, 3]

def f(x):
    x[0] = x[0] + 1
    return x

for i in range(3):
    l.append(x[:])
    x = f(x)

Output:

>>> l
[[1, 2, 3], [2, 2, 3], [3, 2, 3]]

answered Nov 28 '16 at 15:17

ettanany

1 Answers1