Takes array as parameter and returns a reverse array using loop

Question

# Function that takes array as parameter and returns a reverse array 
# using loop

def reverse_list(arr = []):
    for i in arr[::-1]:
        print(i)
arr_num = [1, 2, 3, 4, 5]

print(reverse_list(arr_num))

I want my function to take an array as a parameter, but I'm not sure if the structure /code of it is correct.

https://stackoverflow.com/questions/3940128/how-to-reverse-a-list — Shavk with a Hoon, Jul 16 '22 at 12:46
@BenjaminW., I already get the output that I want. But I want to verify if my code is correct when taking an array as a parameter. — , Jul 16 '22 at 12:48
Your function does not return a list, it only prints the result in reverse — Dani Mesejo, Jul 16 '22 at 12:49
If you want to print the list reversely - you just did. But if you want a *reversed List* - your code did not work. — Daniel Hao, Jul 16 '22 at 12:55

Daniel Hao · Answer 1 · 2022-07-16T13:21:19.440

1

Your function will not work since it's not returning the list.

Here is one way to solve this problem - using the for-loop:

def reverse_list(arr):
    result = []
    
    for i, _ in enumerate(arr):    # try to use enumerate - it's better in most cases
        result.append(arr[~i])     # use the backward indexing here
        
    return result

edited Jul 16 '22 at 13:21

answered Jul 16 '22 at 13:00

Daniel Hao

4,922
3
10
23

XxJames07- · Answer 2 · 2022-08-05T14:18:41.587

1

you can simply use the reversed builtin function;

>>> reversed([1,2,3,4])
[4,3,2,1]

but if you wanted to have a function to return it, i will advise to use the slice indexing:

def rev_list(lst):
    return lst[::-1]

Edit: Use backward indexing,

def rev(lst):
    for i,x in enumerate(list(lst)):
        lst[~i] = x
    return lst

You can do it also by list comprehension:

def reverse(lst):
    return [tmp[i] for i in range(0,len(lst)-1,-1)]

edited Aug 05 '22 at 14:18

answered Jul 16 '22 at 13:04

XxJames07-

1,833
1
4
17

2

I think OP knows that, he's practicing the *for-loop* to learn the language. – Daniel Hao Jul 16 '22 at 13:06
1

I know I can use it. But I want to achieve it using _for loop_ – Jul 16 '22 at 13:06

cards · Answer 3 · 2022-07-16T14:35:33.530

With a list comprehension together with the reversed build-in function (it returns a generator):

def reverse_list(lst):
    return [v for v in reversed(lst)]
    # or return list(reversed(lst))

Another version but without for-loop to highlight the underlying processes:

Using build-in function slice to select a range of items in a sequence object and select an element from the container with __getitem__ subscription.

def reverse_list(lst):
    # slice object
    s = slice(None, None, -1)
    # selection
    return lst.__getitem__(s) # <--> lst[s]

score 0 · Accepted Answer · answered Jul 16 '22 at 12:57

0

Simply create a new array inside the function and either append each values before returning it

def reverse_list(arr = []):
    new_arr = []
    for i in arr[::-1]:
        # print(i)
        new_arr.append(i)
    return new_arr


arr_num = [1, 2, 3, 4, 5]

print(reverse_list(arr_num))

Or in short assign the reversed array to the new array

def reverse_list(arr = []):
    new_arr = arr[::-1]
    return new_arr

answered Jul 16 '22 at 12:57

tebkanlo

148
1
8

2

In the 2nd one - don't need *new_arr* var. just return the *arr[::-1]* would be better. – Daniel Hao Jul 16 '22 at 13:08
You're right, it's just a stylistic habit when the value(s) is too long, just for readability – tebkanlo Jul 18 '22 at 14:16

Takes array as parameter and returns a reverse array using loop

4 Answers4