# Advanced python code challenges : lists part 4 double index

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I am not sure why my code is not correct which is following:
def double_index(lst,index1):
if index1 <= len(lst) and index1 > 0:
lst[index1] = lst[index1] * 2
return lst
else:
return lst
#Uncomment the line below when your function is done
print(double_index([3, 8, -10, 12], 10))

when i check answer on this it says i need to put a check for index is too big:
here is the solution code:
def double_index(lst, index):

# Checks to see if index is too big

if index >= len(lst):
return lst
else:
# Gets the original list up to index
new_lst = lst[0:index]

# Adds double the value at index to the new list

new_lst.append(lst[index]*2)

# Adds the rest of the original list

new_lst = new_lst + lst[index+1:]
return new_lst

#Uncomment the line below when your function is done
print(double_index([3, 8, -10, 12], 10))

if i run the both code it gives me same answer, please advise, also solution code doesnot work for negative numbers, mine does.

Still a beginner, trying to learn!

Hello @harrym2386783121, welcome to the forums! Consider your condition here:

What happens if the index is the same the length of the list? The doubling index code would still run. But wouldn’t that throw an `index out of range` error? Also, can’t a list index be `0`? So the condition `index > 0` would stop the doubling index code from running, even though it would be a valid index.

In future, can you please format code when you post it? To see how to format code, review ->this<- thread.

2 Likes

1. i agree on the same length part, but solution code is not giving the list without doubling the index, also let me fix this with operators.
2. Solution code give error when i put a negative number, mine doesnot.
I know my code has issues Sir, i have started python 3 days ago.

here is my amended code format code:

``````if index1 >= len(lst):
return lst
elif index1 < 0:
return lst
else:
lst[index1] == lst[index1] * 2
return lst
``````

really appreciate the help!

I think that code would work much better now! Just watch out here:

``````lst[index1] == lst[index1] * 2
^^
here there is a comparison operator
``````

You should use the assignment operator (`=`).

That is true.

I believe the solution code is just a longer-winded way of doing it (while also being quite memory expensive-by the fact it creates a whole new list). However, there is some benefits (such as not modifying the input list).

3 Likes

Awesome! thank you for the suggestion!
you guys are really good, hope i’ll be like you guys too

3 Likes

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