Here are 3 simple ways in which you can reverse a Python π list.
Let's see how they are different.![>>> lst = [42, 73, 0] >>> rev1 = reversed(lst) >>> rev2 = ls](/images/1px.png)
Let's see how they are different.
![>>> lst = [42, 73, 0] >>> rev1 = reversed(lst) >>> rev2 = ls](https://pbs.twimg.com/media/Fa_g8XbWQAAKBMr.png)
#1: the built-in `reversed`:
The built-in `reversed` accepts a sequence and returns an object that knows how to iterate over that sequence IN REVERSE.
Hence, `reversed`.
Notice it doesn't return a list:
The built-in `reversed` accepts a sequence and returns an object that knows how to iterate over that sequence IN REVERSE.
Hence, `reversed`.
Notice it doesn't return a list:
The `list_reverseiterator` object that is returned is βlinkedβ to the original list...
So, if you change the original list, the reverse iterator will notice:
So, if you change the original list, the reverse iterator will notice:
![>>> lst = [42, 73, 0] >>> rev = reversed(lst) >>> lst[1] = 9](https://pbs.twimg.com/media/Fa_g934XoAAkYJC.jpg)
#2: slicing with `[::-1]`:
The slicing syntax with brackets `[]` and colons `:` accepts a βstepβ that can be negative.
If the βstartβ and βstopβ are omitted and the βstepβ is -1, we get a copy in the reverse order:
The slicing syntax with brackets `[]` and colons `:` accepts a βstepβ that can be negative.
If the βstartβ and βstopβ are omitted and the βstepβ is -1, we get a copy in the reverse order:
![>>> lst = [42, 73, 0] >>> lst[::-1] [0, 73, 42]](https://pbs.twimg.com/media/Fa_g-gwWAAA3c7o.png)
Slices in Python π are regular objects, so you can also name them.
Thus, you could go as far as creating a named slice to reverse lists, and then use it:
Thus, you could go as far as creating a named slice to reverse lists, and then use it:
![>>> lst [42, 73, 0] >>> reverse = slice(None, None, -1) >>>](https://pbs.twimg.com/media/Fa_g_J_XoAAZxRt.jpg)
Notice that slices are not βlinkedβ to the original list.
That's because slicing creates a copy of the list.
So, if you change the elements in a given index, the reversed list will not notice:
That's because slicing creates a copy of the list.
So, if you change the elements in a given index, the reversed list will not notice:
![>>> lst = [42, 73, 0] # Original list. >>> rev = lst[::-1]](https://pbs.twimg.com/media/Fa_g_2IWYAA6xVS.jpg)
Slicing is very powerful and useful, and that is why I wrote a whole chapter of my free book βPydon'tsβ on the subject.
The link to the free book is in my Twitter profile and the chapter can also be read online:
mathspp.com/blog/pydonts/iβ¦
The link to the free book is in my Twitter profile and the chapter can also be read online:
mathspp.com/blog/pydonts/iβ¦
#3: the method `.reverse`:
Lists have a method `.reverse` that reverses the list IN PLACE.
What this means is that you do not get a return value with the reversed list...
Instead, the list itself gets turned around π
Lists have a method `.reverse` that reverses the list IN PLACE.
What this means is that you do not get a return value with the reversed list...
Instead, the list itself gets turned around π
![>>> lst = [42, 73, 0] >>> lst.reverse() >>> lst [0, 73, 42]](https://pbs.twimg.com/media/Fa_hAi4XgAAT3Q2.png)
There you have it, three ways in which you can reverse a Python list.
I hope this was useful and, if it was, follow me @mathsppblog for more daily Python knowledge π
Extra internet points if you retweet this thread for me π
I hope this was useful and, if it was, follow me @mathsppblog for more daily Python knowledge π
Extra internet points if you retweet this thread for me π
Here is a quick summary:
Reverse a Python list with:
1. the built-in `reversed` that will notice changes to the original list;
2. slicing `[::-1]` that creates a copy of the original list; and
3. the method `.reverse` that reverses a list in place.
Reverse a Python list with:
1. the built-in `reversed` that will notice changes to the original list;
2. slicing `[::-1]` that creates a copy of the original list; and
3. the method `.reverse` that reverses a list in place.
β’ β’ β’
Missing some Tweet in this thread? You can try to
force a refresh
γ
![Diagram showing how you can use f-strings and their format specification to redact private or sensitive information, like email addresses. The code from the diagram: def redact_email(email): user, _, domain = email.partition("@") return f"{user[:2]:*<{len(user)}}@{domain}" print(redact_email("rodrigo@mathspp.com")) # ro*****@mathspp.com](https://pbs.twimg.com/media/GqhlkWbXgAAE9kd.jpg)
