trying to keep the original value of a list python

Question

ignore the code its working perfectly but the problem is when that i have the t list that i need it value for a procedure so what i did is i made a new empty list (aux) and put t values inside of it so the original list doesn't get changed but it still does for some reason this is the code

def listeDesTermes(k):
    Un = 0 
    t = [1,1]
    i=2
    while Un < k:
        Un = t[i-1] + t[i-2]
        t.append(Un)
        i=i+1
    return(t[0:len(t)-1])
#---------------
def Maximal (t) : 
    Maximal = 0
    for i in range(1,len(t)) :
        if t[i] > t[Maximal] :
            Maximal = i
    return(Maximal)
#--------------- 
def DecompsitionK(k,aux):
    s= 0
    Tdecomp = []
    while not k == s :
        maximum = Maximal (aux)
        if s + aux[maximum] <= k :
            s = s+aux[maximum]
            Tdecomp.append(aux[maximum])
            aux[maximum] = -69
        else : 
            aux[maximum] = -69
    return(Tdecomp)
#--------------- 
def conctenationT(t,Tused):
    for i in range(len(t)):
        if t[i] in Tused :
            t[i] = str(t[i])+"1"
        else:
            t[i] = str(t[i])+"0"
#---------------    
t=listeDesTermes(50)
# problem starts here 
aux = t
print(t)
Tused=(DecompsitionK(50,aux))
conctenationT(t,Tused)
print(t)

Mandatory link to [Ned Batchelder](https://nedbatchelder.com/text/names.html) — quamrana, Aug 07 '21 at 20:14
`aux = t` does nothing except make a new variable named `aux`. No Copies Happen Here. — quamrana, Aug 07 '21 at 20:15
Mandatory link to [Ned Batchelder](https://nedbatchelder.com/text/names.html) — quamrana, Aug 07 '21 at 20:16
`aux supposed to get the value of t` <= you're making things up now. — quamrana, Aug 07 '21 at 20:17
Not related to your question, but please consider taking a look at [PEP 8 -- Style Guide for Python Code](https://www.python.org/dev/peps/pep-0008/#whitespace-in-expressions-and-statements). — fsimonjetz, Aug 07 '21 at 20:19
Ok, being confused is allowed here. Please read the link. Its simple. Variables are just named labels which have a reference to an object. Manipulating variables does not change objects. If you want a copy you have to be explicit, eg `aux = t[:]` or `aux = t.copy()` — quamrana, Aug 07 '21 at 20:24

score 1 · Answer 1 · answered Aug 07 '21 at 20:13

1

In python, variables are saved by reference and not by value. Therefore in order to create a copy of an immutable, in your particular case - a list, you must use the method of list - copy(), or the function copy from the module copy. (copy.copy, there is also copy.deepcopy which copies sub-lists as well). You need to edit your code to:

aux = t.copy()

And it should work!

answered Aug 07 '21 at 20:13

Jonathan1609

1,809
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i dont understand why tho – hamdi salim Aug 07 '21 at 20:15
1

Because when you do this you don't work on the original list but on its copy so you don't modify the original one. Please try it out and tell me wether it works or not – Jonathan1609 Aug 07 '21 at 20:16
it works so whats the original – hamdi salim Aug 07 '21 at 20:18
The original is `t`, `aux` is a **copy** of t. – Jonathan1609 Aug 07 '21 at 20:39
Please mark is as solved if it helped you – Jonathan1609 Aug 07 '21 at 20:39

trying to keep the original value of a list python

1 Answers1