W3Schools
w3schools.com › python › ref_list_reverse.asp
Python List reverse() Method
Q&A Python Bootcamp Python Training ... The reverse() method reverses the sorting order of the elements. ... The built-in function reversed() returns a reversed iterator object. ... If you want to use W3Schools services as an educational ...
W3Schools
w3schools.com › python › ref_func_reversed.asp
Python reversed() Function
Python Overview Python Built-in Functions Python String Methods Python List Methods Python Dictionary Methods Python Tuple Methods Python Set Methods Python File Methods Python Keywords Python Exceptions Python Glossary · Built-in Modules Random Module Requests Module Statistics Module Math Module cMath Module · Remove List Duplicates Reverse a String Add Two Numbers
Videos
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20 Ways You Can Reverse List in Python - YouTube
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What "reversed()" ACTUALLY Does In Python - YouTube
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Reverse String in Python: Reverse String in Python using Slicing ...
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How To Reverse A List In Python - YouTube
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Python Interview Prep | Alternate Ways to Reverse a String using ...
Programiz
programiz.com › python-programming › methods › built-in › reversed
Python reversed()
The reversed() function returns an iterator object that provides access to the elements of an iterable (list, tuple, string, etc.) in reverse order. string = 'Python' result = reversed(string) # convert the iterator to list and print it print(list(result)) # Output: ['n', 'o', 'h', 't', 'y', 'P']
W3Schools
w3schools.com › python › python_howto_reverse_string.asp
How to reverse a String in Python
Learn how to reverse a String in Python. There is no built-in function to reverse a String in Python.
Real Python
realpython.com › ref › builtin-functions › reversed
reversed() | Python’s Built-in Functions – Real Python
The built-in reversed() function takes a sequence as an argument and returns an iterator that yields the elements in reverse order.
Programiz
programiz.com › python-programming › methods › list › reverse
Python List reverse()
The reverse() method reverses the elements of the list.
Codecademy
codecademy.com › docs › python › built-in functions › reversed()
Python | Built-in Functions | reversed() | Codecademy
August 22, 2023 - The reversed() function takes in an iterable object, such as a list, string, or a tuple and returns a reversed iterator object. ... Learn to analyze and visualize data using Python and statistics.
Educative
educative.io › answers › how-to-use-the-reverse-and-reversed-methods-in-python
How to use the reverse() and reversed() methods in Python
The reversed() function does not reverse anything but returns an object to iterate over the elements in reverse order.
ThePythonGuru
thepythonguru.com › python-builtin-functions › reversed
Python reversed() function - ThePythonGuru.com
January 7, 2020 - from collections import namedtuple Card = namedtuple('Card', ['rank', 'suit']) class CardDeck: suits = ('club', 'diamond', 'heart', 'spades') ranks = tuple((str(i) for i in range(2, 11))) + tuple("JQKA") def __init__(self): self._cards = [Card(r, s) for s in self.suits for r in self.ranks ] def __len__(self): return len(self._cards) def __getitem__(self, index): return self._cards[index] # def __reversed__(self): this is how you would define __reversed__() method # return self._cards[::-1] deck = CardDeck() print(deck) print( deck[0], deck[-1] ) # deck before reversing reversed_deck = list(reversed(deck)) print(reversed_deck[0], reversed_deck[-1] ) # deck after reversing ... This site generously supported by DataCamp. DataCamp offers online interactive Python Tutorials for Data Science.
GeeksforGeeks
geeksforgeeks.org › python-list-reverse
Python List Reverse() - GeeksforGeeks
April 25, 2025 - It only takes one argument, element ... print(a ... The reverse() method is an inbuilt method in Python that reverses the order of elements in a list....
Real Python
realpython.com › reverse-string-python
Reverse Strings in Python: reversed(), Slicing, and More – Real Python
July 31, 2023 - These features allow you to use slicing to directly generate a copy of a given string in reverse order. The second option is to use the built-in function reversed() to create an iterator that yields the characters of an input string in reverse order.
Educative
educative.io › answers › how-to-use-reverse-in-python
How to use reverse() in Python
The reversed() function takes any sequence as an argument and returns a reversed iterator object. The iterator object accesses the objects of the sequence in reverse order.
GeeksforGeeks
geeksforgeeks.org › python › python-reversed-function
Python reversed() Method - GeeksforGeeks
February 17, 2026 - reversed() function in Python returns an iterator that accesses elements in reverse order. It does not create a new reversed copy of the sequence, making it memory-efficient.
Scaler
scaler.com › home › topics › reversed in python | python reversed() function
Reversed in Python | Python reversed() Function - Scaler Topics
July 5, 2022 - The built-in reversed function in Python is used to reverse a sequence like a list, string, or tuple by creating a reverse iterator of the given sequence.
DataCamp
datacamp.com › tutorial › python-reverse-list
Python Reverse List: How to Reorder Your Data | DataCamp
February 27, 2025 - Solution: Use the reversed() function, which returns an iterator without creating a new list in memory. This is especially useful if you only need to iterate over the list in reverse without storing it. #Python reversed() to save memory with large lists large_list = range(1000000) for item ...
Python.org
discuss.python.org › ideas
Method for reversing strings - Ideas - Discussions on Python.org
February 20, 2025 - I would like to add a .reverse() method for strings. I think most modern languages have something like that and [::-1] is a bit archaic with little charm. There may be other methods like splitting the string, reversing t…
Mimo
mimo.org › glossary › python › list-reverse-method
Python List reverse() Method: Syntax, Methods, and Examples
Learn how to reverse a list in Python using slicing, reverse(), reversed(), and loops. Compare methods, use cases, and performance best practices.
Python.org
discuss.python.org › python help
Beginner question: assigning variable to list.reverse() - Python Help - Discussions on Python.org
May 12, 2022 - Any idea why assigning variable Y to this does not result in anything? create a list of prime numbers x = [2, 3, 5, 7] reverse the order of list elements y=x.reverse() print(y)
Python Forum
python-forum.io › thread-32496.html
Reverse Function in Python
Hi everyone i am beginner in python i am facing with this exercice can anyone explained how to write this in Python : Exercice : ----------------------------- Write a function reverse that receives an integer n as a parameter and returns that in...
Top answer 1 of 2
3
No, this is not possible in Python (or most/any other languages). For any function that does slightly complicated branching or even common math operations, it is completely impossible to undo. One very simple example:
def foo(a, b):
return a + b
foo.undo(6) # made-up example syntax
What should this return? 0 and 6, or maybe -13 and 19? A reversible function needs to have an unambiguous mapping from both input to output and output to input. Anything in the function that would cause two different inputs to create the same output will break this mapping.
Especially in your example, you are utilizing randomness. How could the program even know what to undo if it is randomized? The mapping isn't even consistent for input to output, much less the other way around.
If you want to do something like this, you could use simple substitutions only (such as rot13), which provides a direct mapping between characters. You could also keep track of previous values in a dict with the function results being the keys, which would work because it is creating the mapping as it goes. This obviously would not work on its own across multiple runs of the program though, as it would not preserve the mapping.
Whichever method you choose, you will definitely need to write your own undo function.
2 of 2
1
Many answers have pointed out how what you're describing (reversing the actions of a generic function) is mathematically impossible. I'll show you here a way you could accomplish this under some very specific circumstances, though I will hasten to point out that they are correct -- this will not work in the general case.
However, if you're frequently round-tripping these results, it might be helpful to memoize the results of your hash function and do a reverse lookup.
# This code assumes that the memo dictionary need not be bounded in size.
# A real implementation will likely include a method to cull old results
# once the memo reaches a certain size. See `functools.lru_cache` for a
# specific example of this made for speeding up repeated function calls.
_memo_dict = dict()
def hash(p):
# produces strlist as above, then...
_key = tuple(strlist)
_memo_dict[_key] = p
def unhash(hashed_p: list[int]) -> str:
cache_hit = _memo_dict.get(tuple(hashed_p))
if cache_hit is not None:
# we've previously hashed a string to get this
# value so we can skip the calculations to reverse
# the process and just hand back the result
return cache_hit
# otherwise, you should have some way to reverse it
# manually here.