Why does not the + operator change a list while .append() does? and some slightly longer (and slower) solution: for i in reversed(range(101)) learn more about lists and tuples in this article, Python Data Structures in Practice course. The example below creates a list of a range of numbers Novices often write incorrect code that expects .append (in particular) to return the same list that was just modified. Result: 10 To get modified versions of the list, see: The same issue applies to some methods of other built-in data types, e.g. This built-in function was specially designed to support reverse iteration. If you pass two arguments to the range function, they are interpreted as the start and the stop (in this specific order). Lets see how this works by creating a range that decrements by 1 from 5 to 0: Launching the CI/CD and R Collectives and community editing features for How do you display a list of numbers using a for loop and one int variable? The range () method also allows us to specify where the range should start and stop. For example, Value This refers to the value stored by the object. A Computer Science portal for geeks. When the for structure begins executing, the function range creates a sequence of values, which range from zero to four. See How can I get a sorted copy of a list? You need the base case to end the recursive loop. When in doubt, always remember: if you see three arguments in a range() function call, theyre always the start, the stop, and the step, in this exact order! I'd like to reserve chaining for operations that return new values, Instead, you use lists, and Python offers a few ways to reverse them. What happened to Aham and its derivatives in Marathi? This is obviously a mindset that I need to aim to cultivate, because my initial reaction to "so why return it again?" for i in range(100, -1, -1) Your email address will not be published. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. It will be much simpler than any of the workarounds needed for removing items from the list while iterating over it. The A range object doesnt actually show its elements to you until you explicitly request them. How Do You Write a SELECT Statement in SQL? 4 Like other mutable sequence types, Python lists implement .reverse(). Note that range(6) is not the values of 0 to 6, but the values 0 to 5. Why does Jesus turn to the Father to forgive in Luke 23:34? Heres how you can define a recursive function to return a reversed copy of a given list: Inside reversed_list(), you first check the base case, in which the input list is empty and makes the function return. Additionally, you can also pass an incrementer, the default is set to 1. If we have a section of code that we would like to repeat a certain number of times, we employ for loops. Study the example carefully: y got the special None value, because that is what was returned. The range() function returns a sequence of numbers, starting from 0 by default, and increments by 1 (by default), and ends at a specified number. The range() function allows you to generate a list of numbers within a specified range. for x in range (z): (or debugging questions that boil down to that problem), see Why does "x = x.append()" not work in a for loop?. That sounds complicated, so here are some examples of how slice() works: The first call to slice() is equivalent to [0:len(digits)]. In the example below, we jump downwards 10 values with each iteration: As a bonus, heres another way to reverse a range: use the sorted() function with the parameter reverse=True. Proper way to declare custom exceptions in modern Python? Indexing in Python starts from 0, so the first element has an index of 0, the second element has an index of 1, and so on. Sometimes we have to iterate through the elements in the reverse order. Practice Python if you want to become a programming virtuoso. A common technique is to loop through the first half of it while swapping each element with its mirror counterpart on the second half of the list. Thank you for your input! For example, to reverse the list represented in the diagram, you can loop over the first half of the list In many ways the object returned by range () behaves as if it is a list, but in fact it isnt. For example, provided a number n, range() produces integers from 0 up to n-1. The idea is to get a list and create a copy of it in reverse order. It is an object which returns the successive items of the desired sequence when you iterate over it, but it doesnt really make the list, thus saving space. Early in your Python journey, youll start working with sequences and ranges. No spam ever. 542), How Intuit democratizes AI development across teams through reusability, We've added a "Necessary cookies only" option to the cookie consent popup. The step parameter is the number that determines how numbers will be incremented. There shouldn't be any new UnicodeEncodeError: 'ascii' codec can't encode character u'\xa0' in position 20: ordinal not in range(128). This rev2023.3.1.43269. As it turns out, there are multiple ways of reversing a range in Python. for i in range(len(text)-1, -1, -1): like string processing operations: There are a few standard library modules that encourage chaining of EDIT: I just learned from another answer that this principle is called Command-Query separation. Recursion is when you define a function that calls itself. While using W3Schools, you agree to have read and accepted our. For example. For example, say you need to iterate over a list of numbers in reverse order and replace every number with its square value. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. Get tips for asking good questions and get answers to common questions in our support portal. Python 2.3 extended the syntax to built-in types, so you can use step with them now. Note that .reverse() doesnt return a new list but None: Trying to assign the return value of .reverse() to a variable is a common mistake related to using this method. numbers = (1, 2, 3, 4, 5) for n in reversed (numbers): print (n) Does Cosmic Background radiation transmit heat? But for iteration, you should really be using xrange instead. See Is making in-place operations return the object a bad idea?. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. The goal of .sort() is to sort the items of a list. To get the most out of this tutorial, it would be helpful to know the basics of iterables, for loops, lists, list comprehensions, generator expressions, and recursion. For example, say you want to iterate over a range of floating-point numbers. Heres how you can use reversed() to iterate through the items in a list in reverse order: The first thing to note in this example is that the for loop is highly readable. WebIn Python 3, range behaves the same way as xrange does in 2.7. The same reasoning applies to designing your own APIs. In day-to-day programming, you might find that iterating through existing lists and sequences in reverse order, typically known as reverse iteration, is a fairly common requirement. Lets start with the basics: Pythons range() function is used to produce a sequence of increasing numbers (or decreasing numbers, as we will see below). This makes the comprehension loop iterate over the items in digits in reverse, creating a new reversed list in the process. Reverse Iteration using for Loop and reversed () function The for loop iterates through the sequence elements in the order of their occurrence. Print new line at the end of both internal loops. WebPython Glossary Else in For Loop The else keyword in a for loop specifies a block of code to be executed when the loop is finished: Example Get your own Python Server Print all numbers from 0 to 5, and print a message when the loop has ended: for x in range(6): print(x) else: print("Finally finished!") Unexpected Behavior of Extend with a list in Python, Unable to reverse lists in Python, getting "Nonetype" as list. Note: Python 3 has not separate range and xrange functions, there is just range, which follows the design of Python 2s xrange. Note: To dive deeper into how to use .sort() and sorted(), check out How to Use sorted() and sort() in Python. If so, then this tutorial is for you. Our mission: to help people learn to code for free. Discover how to write custom sort functions in Python, create a custom order in Python, and perform comparisons in Python. Another solution: z = 10 How do I move list elements to another list if a condition is met? Not the answer you're looking for? Yes. The slicing operator works similarly to the range() function you saw earlier on. We can traverse a list in Python in reverse order by using the inbuilt reversed () function available. You can also take advantage of .insert() to create reversed lists with the help of a loop: The call to .insert() inside the loop inserts subsequent items at the 0 index of result. If a law is new but its interpretation is vague, can the courts directly ask the drafters the intent and official interpretation of their law? Then you store the resulting iterator in reversed_digits. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. Why does append() always return None in Python? Don't confuse this with the .reverse() method! Asking for help, clarification, or responding to other answers. Python Lists, Tuples, and Sets: Whats the Difference? The syntax of the reverse () method is as follows: list.reverse() reverse () doesnt accept arguments. This slicing returns all the items in the target range because step defaults to 1. Degree in Computer Science and Engineer: App Developer and has multiple Programming languages experience. When you want to print all items, you use one of the two following ways: So, you either use one or two colons to output all items contained in the list. If you dont provide values to start and stop, then they are set to 0 and to the length of the target sequence, respectively. Your learning journey is just beginning! print n Why is "1000000000000000 in range(1000000000000001)" so fast in Python 3? Most of the time, youll use it to equip your own classes with reverse iteration capabilities. See also How to allow list append() method to return the new list for .append and How do I concatenate two lists in Python? sentence = input ("Input a word to reverse: ") for char in range (len (sentence) - 1, -1, -1): print (sentence [char], end="") print ("\n") Output: Reverse only letters in word main.py WebThe range () function in Python 3 is a renamed version of the xrange (). Is making in-place operations return the object a bad idea? 3 Leave a comment below and let us know. However, the same tools and techniques apply to lists of any type of Python objects, such as lists of strings. Another point to note is that you cant use reversed() with unordered iterables: In this example, when you try to use reversed() with a set object, you get a TypeError. On the other hand, immutable doesnt allow any change in the object once it has been created. on a single object can be chained like this: I find the chaining form a threat to readability; it requires that the With a list as an argument, it returns an iterator that yields the input list items in reverse order. print y How can I access environment variables in Python? WebWe can use the Python range method itself to return a sequence in reverse order, rather than in increasing order. How are you going to put your newfound skills to use? As we know list in python is a mutable object and one of characteristics of mutable object is the ability to modify the state of this object without the need to assign its new state to a variable. range () function: Using a for loop with range (), we can repeat an action a specific number of times while loop: To repeat a block of code repeatedly, as long as the condition is true. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. This of course is even more true if you don't actually loop over the whole list, and it stops being true if you use the list more than once. To do that, you can pass True to their respective reverse argument. Each iteration swaps an item from the first half of the list with its mirror counterpart in the second half. At the end of the loop, you get a new list with the items of a_list in reverse order. See also A quick way to return list without a specific element in Python. So. Theoretically Correct vs Practical Notation. However, that syntax initially didnt work on built-in types, such as lists, tuples, and strings. The range goes from 5 (the start) up to 0 (the stop), but with a step of -1, meaning that the numbers decrease. (look at pattern above) Spaces will be printed for size - i times and stars will be printed for i times. Try range(100,-1,-1) , the 3rd argument being the increment to use (documented here ). ("range" options, start, stop, step are documented here ) which is the recommended method depending on situation? It contains well written, well thought and well explained computer science and programming articles, quizzes and practice/competitive programming/company interview Questions. WebInside the outer loop, the 1st inner loop handles the number of spaces and the values change according to requirements. object, and so even if you don't know the class and its methods very range() and xrange() take a third parameter that specifies a step. How to extract the coefficients from a long exponential expression? One could argue that the signature itself makes it clear that the function mutates the list rather than returning a new one: if the function returned a list, its behavior would have been much less obvious. If thats your case, then you have several options. Each tutorial at Real Python is created by a team of developers so that it meets our high quality standards. why does python's list.append evaluate to false? Just use y = []. Why was the nose gear of Concorde located so far aft? start: It is the starting index of the sequence. You cant use range(), so you decide to create your own class to approach this specific use case. (If you plan to remove multiple elements, strongly consider using a list comprehension (or filter) instead. I'm dealing with a list of about 5e6 elements or so, so I really need to avoid copying the list. Heres a table that summarizes the more important points youve already covered: A quick look at this summary will allow you to decide which tool or technique to use when youre reversing lists in place, creating reversed copies of existing lists, or iterating over your lists in reverse order. There are multiple use cases for Python range reverse and hence it is important that you know how this can be achieved. But what if you need these values in the reverse order? It works just like you would expect: In the example above, range() has a default start of 0 and a stop of 5, so it goes from 0 to 4. As a function: (We can translate .pop similarly to make a modified copy, though of course .pop actually returns an element from the list.). Heres an example of how to use a list comprehension to create a reversed list: The magic in this list comprehension comes from the call to range(). Dealing with hard questions during a software developer interview. Python code: def PalindromeComparator(original): for i Note: The example above uses a wasteful technique because it creates several lists only to throw them away in the next iteration. This call removes and returns the last item in the list, so you can store it in last_item. If youre working with lists in Python, then you probably want to consider using a list comprehension. If you pass True to its reverse keyword argument, then you get a reversed copy of the initial list: The reverse argument to sorted() allows you to sort iterables in descending order instead of in ascending order. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. This comes from a coding style (popular in various other languages, I If you use a different step, then the slicing jumps as many items as the value of step: In the first example, [0::2] extracts all items from index 0 to the end of digits, jumping over two items each time. for details. I wish my past-self had thought to include the link to "comments by Guido" :( also, Tim, your first link to "another answer" also links to the Wikipedia page (though I suspect that you, too, currently lack the context to correct that). k = 100 - i Your email address will not be published. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. You also need to define the recursive case, which reduces all successive cases toward the base case and, therefore, to the loops end. A Computer Science portal for geeks. The range () function executes a group of statements for a specified number of times. reversed should be best as it returns an iterator, so it doesn't copy the list, just yields one element at a time. Let's take our very first example, where we used range (5). Can I use this tire + rim combination : CONTINENTAL GRAND PRIX 5000 (28mm) + GT540 (24mm), Drift correction for sensor readings using a high-pass filter. Free Bonus: Click here to get a Python Cheat Sheet and learn the basics of Python 3, like working with data types, dictionaries, lists, and Python functions. Why is "1000000000000000 in range(1000000000000001)" so fast in Python 3? When it comes to reversing lists, the base case would be reached when the recursive calls get to the end of the input list. print("reverse({}): Has 90% of ice around Antarctica disappeared in less than a decade? Heres how you can use slice() to create a reversed copy of an existing list: The slice object extracts all the items from digits, starting from the right end back to the left end, and returns a reversed copy of the target list. And even reversed(reversed([1,2,3])) raises TypeError. This may not sound very exciting at first, but range() is useful in many contexts some of which we will explore later in this article. If you are using this method to count back i Webhow to reverse a string in list by for loop code example. If you wanted to store the return value from the reversed() function for later use, you'd instead have to enclose it inside the list() constructor and assign the new list to a variable, like so: And there you have it - you now know the basics of how reversing lists in Python works! reversed = '' WebSee also How to allow list append() method to return the new list for .append and How do I concatenate two lists in Python? mylist.reverse().append('a string')[:someLimit]). In my opinion, this is the most readable: for i in reversed(xrange(101)): All of this knowledge helps you improve your list-related skills. Method 2: Python loop through a list using for loop and range () Another way to loop through a list is by using for loop with the range () function. Still, it provides a quick way to iterate over a reversed copy of an existing list without the risk of being affected by changes in the original list. Let's consider .sort first. Now, how can you reverse a list in place by hand? Note for Python 3 users: There are no separate range and xrange functions in Python 3, there is just range, which follows the design of Python 2's xrange. This knowledge will complement and improve your list-related skills and make you more proficient with them. Rename .gz files according to names in separate txt-file. Should I include the MIT licence of a library which I use from a CDN? The call to enumerate() provides ascending zero-based indices for each item in the reversed copy. however it is possible to specify the increment value by adding a third parameter: range(2, 30, 3): Increment the sequence with 3 (default is 1): Get certifiedby completinga course today! Although using reversed () is one of the easiest ways to reverse a range in Python, it is far from being the only one. For instance, you can also pass a negative step argument into the range () function: See how it works? The range goes from 5 (the start) up to 0 (the stop), but with a step of -1, meaning that the numbers decrease. AllPython Examplesare inPython3, so Maybe its different from python 2 or upgraded versions. Since the range() function returns each number lazily, it is commonly used in for loops. In the example below, we call reversed () on the range object. To calculate this expression the append function will run and the result of expression will be [None, x] and by specifying that you want the second element of the list the result of [None,x][1] will be x. This way also naturally gives a modified copy.). Webhow to reverse a string in list by for loop code example. Negative values can be passed as an increment in order to decrement the output. Up to this point, youve learned a lot about reversing lists using different tools and techniques. This built-in function returns a new list containing all the items of the input iterable in order. Print '*' based on j. basics Besides the above algorithm, which takes advantage of index substitution, there are a few different ways to reverse lists by hand. We also have thousands of freeCodeCamp study groups around the world. However, unlike other programming languages, arrays aren't a built-in data structure in Python. function always returns a WebI can think of some ways to do so in python (creating a list of range(1,n+1) and reverse it, using while and --i, ) but I wondered if there's a more elegant way to do it. Copyright 2014EyeHunts.com. 542), How Intuit democratizes AI development across teams through reusability, We've added a "Necessary cookies only" option to the cookie consent popup. What's the fastest way to iterate over a list in reverse? If you want to learn more about Python, freeCodeCamp offers a Python certification. Join us and get access to thousands of tutorials, hands-on video courses, and a community of expertPythonistas: Master Real-World Python SkillsWith Unlimited Access to RealPython. What does a search warrant actually look like? Leodanis is an industrial engineer who loves Python and software development. How do I get the number of elements in a list (length of a list) in Python? Xcode Build Optimization: A Definitive Guide, Introduction to Functional Programming using Swift, Scale - Royalty-free vector illustrations. The third offset, step, defaults to 1, which is why a normal slicing operation extracts the items from left to right: With [1:5], you get the items from index 1 to index 5 - 1. As a result, numbers ends up containing square values in reverse order. After decrementing the k value, the 2nd inner loop handles the number of columns and the values change according to the outer loop. The next iteration takes 8 and moves it to index 1, and so on. The stop parameter is the number up to but not including the one where the counting will stop. Acceleration without force in rotational motion. How to properly visualize the change of variance of a bivariate Gaussian distribution cut sliced along a fixed variable? Method #1 : Using reversed () The simplest way to perform this is to use the reversed function for the for loop and the iteration will start occurring from the rear side Identity This refers to the address that the object refers to in the computers memory. This way, changes on the input list dont affect the copy. WebReverse a List using For Loop To reverse a list of elements in Python, iterate over the list from the end to start, and append each of the iterated element in a new list. Example 1: python reverse range my_list = [1, 2, 3] my_list. However, its affected by changes in the input list. How to iterate over rows in a DataFrame in Pandas. In short, thats one way to reverse a range in Python! So, reversed() doesnt work for them. The item with the index equal to stop is never included in the final result. x (and that all calls are made for their side-effects), and not to However, you need to explicitly declare the reversed output as a list. Find out how to reverse a range in Python and learn more about the range(), reversed(), and sorted() functions. Reversing and working with lists in reverse order might be a fairly common task in your day-to-day work as a Python coder. What are examples of software that may be seriously affected by a time jump? Input: start = 4, end = 15 Output: 4, 6, 8, 10, 12, 14 Input: start = 8, end = 11 Output: 8, 10 Example #1: Print all even numbers from the given list using for loop Define start and end limit of range. Traversal is the process of iterating across a series. To make an actual copy, simply pass that iterator to list: y = list(reversed(x)). means values from 2 to 6 (but not including 6): The range() function defaults to increment the sequence by 1, , and so on has been created what are examples of software that may be affected... Python in reverse order, rather than in increasing order high quality standards doesnt work them. Loop code example ' ) [: someLimit ] ) Introduction to Functional programming Swift. Follows: list.reverse ( ) function executes a group of statements for a specified number of times example. To lists of strings bad idea?, or responding to other answers be much than! Decrement the output in a DataFrame in Pandas start, stop, step are documented )... Iterable in order to decrement the output: Python reverse range my_list [! Your own class to approach this specific use case object doesnt actually show its elements to list. Pattern above ) Spaces will be printed for I times and stars will be printed size! Comprehension loop iterate over the items in the order of their occurrence ( [ 1,2,3 ] ) 100 I... There are multiple python reverse for loop range of reversing a range in Python, getting Nonetype!, which range from zero to four of times, we employ loops... Out, there are multiple use cases for Python range method itself to return a sequence of values, range!, privacy policy and cookie policy classes with reverse iteration using for code. Changes in the input iterable in order is commonly used in for loops to learn more Python. And make you more proficient with them now y got the special None value, because that what! Python 2.3 extended the syntax of the input list it contains well written, well thought well... Examplesare inPython3, so Maybe its different from Python 2 or upgraded versions will! A time jump, simply pass that iterator to list: y = list ( reversed ( ) reverse {. What happened to Aham and its derivatives in Marathi list with the index equal to is. Degree in Computer Science and programming articles, quizzes and practice/competitive programming/company interview questions I. Offers a Python certification be using xrange instead and hence it is important that you know how can. Equip your own classes with reverse iteration syntax of the list thats one to! ) doesnt work for python reverse for loop range outer loop, you get a new list containing all the items a! The value stored by the object a bad idea? Behavior of Extend with list!, creating a new reversed list in the target range because step to. You to python reverse for loop range a list of numbers in reverse, creating a new list containing all the items the... Every number with its square value iterator to list: y = list ( length of list. Freecodecamp offers a Python coder, such as lists of any type of Python objects, such lists! Webinside the outer loop so I really need to iterate over a list in Python copying the list so. Environment variables in Python, we employ for loops youll use it to equip own! This slicing returns all the items of a library which I use from a CDN return None in Python Unable. Include the MIT licence of a bivariate Gaussian distribution cut sliced along a variable. Fast in Python is when you define a function that calls itself the... In the reverse ( ) always return None in Python common questions in our support portal generate a list numbers..., provided a number n, range behaves the same tools and techniques to. To Aham and its derivatives in Marathi idea is to sort the items the... Order by using the inbuilt reversed ( ) does nose gear of Concorde so! Affect the copy. ), Scale - Royalty-free vector illustrations using xrange instead sorted of! So I really need to avoid copying the list while iterating over it list.reverse ( is. Of reversing python reverse for loop range range in Python, create a custom order in Python digits in order., which range from zero to four values can be achieved when the loop! Do I get the number of Spaces and the values 0 to 6 but... The syntax of the time, youll use it to equip your own class to approach this use. Developer interview `` range '' options, start, stop, step are documented ). ) provides ascending zero-based indices for each item in the reversed copy. ) the default is set to.. Why was the nose gear of Concorde located so far aft the 1st inner loop handles number! Another list if a condition is met { } ): has 90 % of ice around disappeared... ) your email address will not be published Scale - Royalty-free vector illustrations modern Python exceptions. This RSS feed, copy and paste this URL into your RSS reader it... Copy, simply pass that iterator to list: y got the special None,! Object once it has been created interview questions articles, quizzes and practice/competitive programming/company interview questions here ) is!: App Developer and has multiple programming languages, arrays are n't a built-in data in! Of statements for a specified range so on any change in the input list sequence of values, range... Range creates a sequence in reverse order by using the inbuilt reversed ( function. Argument being the increment to use in short, thats one way to over! Same way as xrange does in 2.7 ) in Python, create a copy of list. Loves Python and software development the last item in the second half counterpart the. To do that, you can also pass a negative step argument into the range ( 6 ) is sort! Pass that iterator to list: y = list ( reversed ( ) function you saw earlier.... Probably want to learn more about Python, then you probably want to learn more about,. 100, -1 ), the function range creates a sequence of values which. Built-In data structure in Python, getting `` Nonetype '' as list each in... You should really be using xrange instead which range from zero to.! Early in your Python journey, youll start working with lists in Python, a... I really need to avoid copying the list interview questions of Concorde so. To iterate over a list ) in Python, Unable to reverse a string in by... Condition is met consider using a list of numbers within a specified number of.. Allows us to specify where the range should start and stop this built-in function was specially to... A fixed variable simpler than any of the input list so on when you define a that... We used range ( 5 ) help people learn to code for free to.! Stack Exchange Inc ; user contributions licensed under CC BY-SA ( [ 1,2,3 ] ).... We would Like to repeat a certain number of columns and the values according... Ends up containing square values in reverse order the item with the (! List elements to another list if a condition is met, and Sets: Whats Difference! Be passed as an increment in order to decrement the output reverse order the loop... Of a list comprehension change in the object a bad idea? extended... One where the range ( ) is not the values change according to names in separate txt-file variable! Discover how to Write custom sort functions in Python, then this tutorial is for you as of!: to help people learn to code for free ( `` range '',. Day-To-Day work as a Python coder to do that, you can pass to. Default is set to 1 step defaults to 1 for instance, you agree have! Order of their occurrence the list ( 6 ) is to get a and. To subscribe to this point, youve learned a lot about reversing using. Your newfound skills to use loop iterates through the elements in the input list about Python, freeCodeCamp offers python reverse for loop range... The 2nd inner loop handles the number up to n-1 result, numbers up! Most of the input iterable in order common questions in our support.... The Father to forgive in Luke 23:34 traverse a list ( length a... Multiple programming languages, arrays are n't a built-in data structure in,... Programming virtuoso provides ascending zero-based indices for each item in the reversed copy..! Carefully: y = list ( reversed ( ) doesnt accept arguments - I your email address not. How it works become a programming virtuoso be achieved string in list by for loop code example numbers reverse! Into the range should start and stop even reversed ( [ 1,2,3 ] ) ) raises TypeError going to your. Up to but not including the one where the range ( python reverse for loop range ) } ): has 90 of... Creates a sequence of values, which range from zero to four W3Schools! Mutable sequence types, such as lists of strings is commonly used in for loops coder. Languages, arrays are n't a built-in data structure in Python to built-in types such! Length of a list ( reversed ( ) always return None in Python python reverse for loop range range... Need to avoid copying the list it in last_item end of both internal loops modified copy. ) which. 1: Python reverse range my_list = [ 1, 2, 3 ] my_list Like repeat.