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Shady Habashy
2,139 PointsHi.. I tried the .reverse() method but it always returns ==> None why is this happening ?
Hi.. I tried the .reverse() method to reverse my list but it always returns ==> None why is this happening ?
Shady Habashy
2,139 Pointsmy_list = [1, 2, 3, 4, 5]
rev_list = my_list.reverse()
print(rev_list)
2 Answers
Josh Keenan
19,652 PointsSo list.reverse() uses in place modification, what this means is that the method does not return a new object and instead modifies the already existing one.
So if you want to create a new list object that is the reversed version of your original list, use reversed() and pass in your list, this will create a new object.
my_list = [1, 2, 3, 4, 5]
my_list.reverse()
print("list now: " + str(my_list))
This is what you must to if you want to use list.reverse()
Shady Habashy
2,139 Pointsok got it . Thank you :)
jessicamurr
3,313 PointsHi there! Thanks for answering the same question I had. However, I'm a bit confused. Why do we have to use str() for my_list. I know that not using it makes the return None or have an error pop up, but I'm confused as to why we have to make a list a string. Thanks ahead of time!
Jay zhang
4,109 Pointshello, just to answer the jessicamurr's question, if you test the code you can quickly understand that :
You can only concatenate same value to each other, in this case since "list now: " is a string, you can't concatenate a list to a string
Muhammad khan
Python Development Techdegree Student 1,836 Pointscan someone please explain why am I not getting a reversed list printed? getting some strange out: <list_reverseiterator object at 0x7feb3cf019b0>
my_list = [1, 2, 3, 4, 5]
reversed_list = reversed(my_list)
print(reversed_list)
Alfonso Quijano
15,137 Pointstry "reversed ()" like this: "obj = [6, 7, 8, 9, 10] inverted = reversed (obj) print (inverted) " and I got this result that I understand was stored in that place but it doesn't show me the inverted list. "<list_reverseiterator object at 0x00000268A9B44E20>"
Josh Keenan
19,652 PointsMuhammad khan you need to do
my_list.reverse()
Leonard Peris
15,784 PointsMuhammad khan if you want to obtain a list that is the reverse of your list, without modifying your existing list, see the following code example.
my_list = [1, 2, 3, 4, 5]
reverse_list = list(reversed(my_list))
print(reverse_list)
reversed() returns a <list_reverseiterator object>. In order to obtain a list, we have to pass the return value to list().
Alternatively, you can use slices to obtain the reverse of a list without modifying the original.
my_list = [1, 2, 3, 4, 5]
reverse_list = my_list[::-1]
print(reverse_list)
Josh Keenan
19,652 PointsJosh Keenan
19,652 PointsCan you post some code please so I can try and understand what's going on.