{"id":927,"date":"2022-12-03T13:27:00","date_gmt":"2022-12-03T07:57:00","guid":{"rendered":"https:\/\/geekpython.in\/?p=927"},"modified":"2023-08-26T10:50:46","modified_gmt":"2023-08-26T05:20:46","slug":"different-ways-to-reverse-a-python-list","status":"publish","type":"post","link":"https:\/\/geekpython.in\/different-ways-to-reverse-a-python-list","title":{"rendered":"8 Different Ways To Reverse A Python List"},"content":{"rendered":"\n

Lists are one of the in-built data types in Python and fall into the sequence category. That means lists are used for working with the sequence of objects and we can say a sequence is a Python list when they are wrapped within ([ ]<\/code>) square brackets.<\/p>\n\n\n\n

Just like other data types, lists have numerous methods and function which helps us in modifying and manipulating the elements inside the list.<\/p>\n\n\n\n

Python list has a function named reverse()<\/code> which is used to reverse the elements of the list<\/strong>.<\/p>\n\n\n\n

But in this article, you\u2019ll see the various ways to reverse the elements specified inside the list. The list.reverse()<\/code> function is one you might know but you\u2019ll also see other ways to perform the same operation.<\/p>\n\n\n\n

<\/a>Using list.reverse()<\/strong><\/h1>\n\n\n\n

Python list.reverse()<\/code> used to reverse the elements specified inside the list<\/strong>. If you notice that it is list.reverse<\/code>, this function is specific to Python lists and cannot be used for other data types.<\/p>\n\n\n\n

In the following example, a list is defined and stored in the my_lst<\/code> variable and then performed the reverse operation. This will reverse the order of the elements.<\/p>\n\n\n\n

# Defining a list\nmy_lst = ['a', 'e', 'i', 'o', 'u']\n\n# Using reverse function\nmy_lst.reverse()\nprint(my_lst)<\/pre><\/div>\n\n\n\n
Output<\/strong><\/p>\n\n\n\n
['u', 'o', 'i', 'e', 'a']<\/pre><\/div>\n\n\n\n
Note<\/strong>: If you try to reverse any data type other than lists, an AttributeError<\/code> will be raised stating that \u2018x\u2019 has no attribute \u2018reverse\u2019<\/strong>.<\/p>\n\n\n\n
<\/a>Using reversed()<\/strong><\/h1>\n\n\n\n
Python reversed()<\/code> function is also used to reverse the elements inside the list. Still, instead of returning the reversed object, it returns the reversed iterator object that accesses the values of a given sequence<\/strong>. To access the values, you have to iterate them either by using the for<\/code> loop or the next()<\/code> function.<\/p>\n\n\n\n
Consider the following example, the list object my_lst<\/code> is reversed and then accessed the values using the next()<\/code> function from the reversed iterator object new_lst<\/code>.<\/p>\n\n\n\n
# Defining a list\nmy_lst = ['a', 'e', 'i', 'o', 'u']\n\nnew_lst = reversed(my_lst)\n# Iterating over the reversed iterator obj\nprint(next(new_lst))\nprint(next(new_lst))\nprint(next(new_lst))\nprint(next(new_lst))\nprint(next(new_lst))<\/pre><\/div>\n\n\n\n
Output<\/strong><\/p>\n\n\n\n
u\no\ni\ne\na<\/pre><\/div>\n\n\n\n
One main thing is Python reversed()<\/code> isn\u2019t like the list.reverse()<\/code> function because it can be used for any iterable sequence.<\/p>\n\n\n\n
<\/a>Using list comprehension<\/strong><\/h1>\n\n\n\n
Using list comprehension for reversing the list is different from the approach you\u2019ve seen in the above two ways.<\/p>\n\n\n\n
# Defining a list\nmy_lst = ['a', 'e', 'i', 'o', 'u']\n\n# Taking the index value\nindex = len(my_lst) - 1\n\n# Using list comprehension\nrev_list = [my_lst[i] for i in range(index, -1, -1)]\nprint(rev_list)<\/pre><\/div>\n\n\n\n
In the above Python program, a list is defined and then the variable index<\/code> is defined that stores the list\u2019s index value by taking the list\u2019s length minus 1. Then created a list comprehension<\/strong> that accesses each index item of the list using the range function from the<\/strong> index<\/code> to the end of the list in reverse order<\/strong>.<\/p>\n\n\n\n
Output<\/strong><\/p>\n\n\n\n
['u', 'o', 'i', 'e', 'a']<\/pre><\/div>\n\n\n\n
<\/a>Using for loops<\/strong><\/h1>\n\n\n\n
Python for<\/code> loop is a great way to iterate over a sequence. Let\u2019s see how to reverse a list using the for<\/code> loop.<\/p>\n\n\n\n
# Defining a list\nmy_lst = ['a', 'e', 'i', 'o', 'u']\n# Defining an empty list\nrev_list = list()\n\n# Iterating each element from the original list\nfor elem in my_lst:\n    rev_list = [elem] + rev_list\n\nprint(rev_list)<\/pre><\/div>\n\n\n\n
First, we defined two lists, one is our original list (my_lst<\/code>) and the other is the empty list (rev_list<\/code>) to store the reversed elements.<\/p>\n\n\n\n
Then we iterated over each element from the original list and added them to our empty list named rev_list<\/code>. The output will be a reversed version of the original list.<\/p>\n\n\n\n
Output<\/strong><\/p>\n\n\n\n
['u', 'o', 'i', 'e', 'a']<\/pre><\/div>\n\n\n\n
If you are wondering how it happened, then look at the example below<\/p>\n\n\n\n
for elem in my_lst:\n    rev_list = [elem] + rev_list\n    print(rev_list)<\/pre><\/div>\n\n\n\n
If we print rev_list<\/code> each time the elements from the original list are added then at the end we\u2019ll get the reversed list.<\/p>\n\n\n\n
['a']\n['e', 'a']\n['i', 'e', 'a']\n['o', 'i', 'e', 'a']\n['u', 'o', 'i', 'e', 'a']<\/pre><\/div>\n\n\n\n
<\/a>Using reverse list indexing<\/strong><\/h1>\n\n\n\n
The elements in Python lists have an index value that helps access the specific element. The index value starts with 0<\/code> to n-1<\/code>. List indexing can be done using the format [start : stop: step]<\/code>.<\/p>\n\n\n\n
For example, [: : 1]<\/code> will return the whole list from start to end. Similarly, [: : -1]<\/code> will return the whole list but in reversed order. Let\u2019s see an example.<\/p>\n\n\n\n
# Defining a list\nmy_lst = ['a', 'e', 'i', 'o', 'u']\n\nnew_list = my_lst[: : -1]\nprint(new_list)<\/pre><\/div>\n\n\n\n
The above code will step over the elements from the original list in reverse order.<\/p>\n\n\n\n
['u', 'o', 'i', 'e', 'a']<\/pre><\/div>\n\n\n\n
<\/a>Using slice method<\/strong><\/h1>\n\n\n\n
Python has a function named slice()<\/code> that returns a slice object, which specifies how to slice a sequence. It takes 3 arguments (start, stop, step<\/code>). start<\/code> that specifies from where to start slicing, stop<\/code> that specifies where to end and step<\/code> that specifies the step of the slicing.<\/p>\n\n\n\n
# Defining a list\nmy_lst = ['a', 'e', 'i', 'o', 'u']\n\n# Using the slice method\nreverse = slice(None, None, -1)\n\nnew_list = my_lst[reverse]\nprint(new_list)<\/pre><\/div>\n\n\n\n
In the above program, created a slice object that reverses the order of the original list and is then used to reverse the original list.<\/p>\n\n\n\n
['u', 'o', 'i', 'e', 'a']<\/pre><\/div>\n\n\n\n
<\/a>Using range function<\/strong><\/h1>\n\n\n\n
# Defining a list\nmy_lst = ['a', 'e', 'i', 'o', 'u']\n\n# Accessing the last index value\nindex = len(my_lst)-1\n\n# Using range function\nfor elem in range(index, -1, -1):\n    print(my_lst[elem], end=\" \")<\/pre><\/div>\n\n\n\n
In the above Python program, we are using a range()<\/code> function that is grabbing the last index value of the item and going all the way to the end in the reverse order. It is just like what we\u2019ve done using list comprehension.<\/p>\n\n\n\n
u o i e a<\/pre><\/div>\n\n\n\n
<\/a>Using __reversed__()<\/strong><\/h1>\n\n\n\n
Python list has a special method called __reversed__()<\/code> that helps in reverse iteration. If you remember we saw the reversed()<\/code> function, basically it runs the __reversed__()<\/code> method in the backend to reverse the input list.<\/p>\n\n\n\n
# Defining a list\nmy_lst = ['a', 'e', 'i', 'o', 'u']\n\nnew_list = my_lst.__reversed__()\n\n# Iterating over the reversed object\nfor elem in new_list:\n    print(elem, end=\" \")<\/pre><\/div>\n\n\n\n
Output<\/strong><\/p>\n\n\n\n
u o i e a<\/pre><\/div>\n\n\n\n
<\/a>Conclusion<\/strong><\/h1>\n\n\n\n
You\u2019ve learned the various ways that you can use to reverse the Python lists. Some of the ways you might already know and some don\u2019t.<\/p>\n\n\n\n
Let\u2019s recall the methods you\u2019ve learned in this article to reverse the list:<\/p>\n\n\n\n