Python | Reversing a List

Python provides us with various ways of reversing a list. We will go through few of the many techniques on how a list in python can be reversed.
Examples:

Input : list = [10, 11, 12, 13, 14, 15]
Output : [15, 14, 13, 12, 11, 10]

Input : list = [4, 5, 6, 7, 8, 9]
Output : [9, 8, 7, 6, 5, 4]

Method 1: Using the reversed() built-in function.
In this method, we neither reverse a list in-place(modify the original list), nor we create any copy of the list. Instead, we get a reverse iterator which we use to cycle through the list.



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# Reversing a list using reversed()
def Reverse(lst):
    return [ele for ele in reversed(lst)]
      
# Driver Code
lst = [10, 11, 12, 13, 14, 15]
print(Reverse(lst))

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Output:

[15, 14, 13, 12, 11, 10]

Method 2: Using the reverse() built-in function.
Using the reverse() method we can reverse the contents of the list object in-place i.e., we don’t need to create a new list instead we just copy the existing elements to the original list in reverse order. This method directly modifies the original list.

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# Reversing a list using reverse()
def Reverse(lst):
    lst.reverse()
    return lst
      
lst = [10, 11, 12, 13, 14, 15]
print(Reverse(lst))

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Output:

[15, 14, 13, 12, 11, 10]

Method 3: Using the slicing technique.
In this technique, a copy of the list is made and the list is not sorted in-place. Creating a copy requires more space to hold all of the existing elements. This exhausts more memory.

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# Reversing a list using slicing technique
def Reverse(lst):
    new_lst = lst[::-1]
    return new_lst
      
lst = [10, 11, 12, 13, 14, 15]
print(Reverse(lst))

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Output:

[15, 14, 13, 12, 11, 10]

To get a better understanding on the slicing technique refer Slicing Techniques in Python.



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