Working walrus clear solution for Sort by Extension by carel.anthonissen - python coding challenges

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Working walrus solution in Clear category for Sort by Extension by carel.anthonissen

def sort_by_ext(files):
    skey = lambda s: (bool(s[:(i:=s.rfind('.'))]), s[i+1:], s[:i])
    return sorted(files,key=skey)

May 7, 2020

Comments:

vincentvvasquez1 on July 6, 2020, 5:19 p.m.
Not clear at all!!!

carel.anthonissen on July 7, 2020, 6:08 a.m.
Would it have helped if I added this? ``` <h1>Create the following key for sorting the list</h1> <h1>skey = (has no extension, extension, name)</h1> ```

frewdr_b1604fbe20394abf9f18697 on Aug. 2, 2020, 3:26 a.m.
Thank you for the explanation. Very clean.

Dubeb on Sept. 28, 2020, 4:26 p.m.
Great code, pretty straightforward. Just one question, what does the "bool()" serve for ? wouldn't that expression be a boolean anyway ?

carel.anthonissen on Sept. 29, 2020, 6:48 a.m.
The expression does not yield a bool, but the position of the "." in the string. The first element of the key sorts by whether or not the string has an extension. Without the bool, it will sort by the position of the "." in the string and override subsequent elements of the key.

larasing83 on Oct. 5, 2020, 5:37 a.m.
This doesn't seem to work in Python 3.6? Python Tutor which runs on Python 3.6 returned Syntax error

carel.anthonissen on Oct. 5, 2020, 7:18 p.m.
Yup, the walrus operator was introduced in python 3.8.

filonich.v on Oct. 27, 2020, 8:46 p.m.
Need to be careful with s.rfind though. In the following example [".config", "config", "no.name.", "no.name", "abc", "a"] it won't sort right because "abc".rfind(".") = -1 and the "has extension" flag will misreturn True.

carel.anthonissen on Dec. 10, 2020, 5:29 a.m.
You are right. The solution assumes that the names without extensions end with ".". It does not work for names that do not contain "." and it seems the problem description does not require this, so it is an edge case that is unaccounted for.

CakeForDrake on Dec. 9, 2020, 5:40 p.m.
are you Korean or what?

carel.anthonissen on Dec. 10, 2020, 4:44 a.m.
Strange question. Why are you asking?

nazarstakhovskyi on June 11, 2021, 6:42 a.m.
A great solution, thanks a lot! Can anybody tell me, though, why we need the bool() in here? I can see that it doesn't work without it, but can't quite understand why

K_at_play on July 15, 2021, 1:40 a.m.
Without bool() the sorting rule is equivalent to the last sort - "s[:i]". Let's take the ".something" file name where the whole string is a name and extension is empty. In this case, s[:i] is an empty string, so bool(s[:i]) returns False (sorts the file to the beginning of the list). Without it the file name would be treated by the algorithm as an empty name with the ".something" extension.

K_at_play on July 15, 2021, 1:08 a.m.
Great solution! To make it shorter, "+1" in "s[i+1:]" could be removed and the "skey" declaration could be moved to the return line. <pre class='brush: python'>def sort_by_ext(files): return sorted(files,key=lambda s: (bool(s[:(i:=s.rfind('.'))]), s[i:], s[:i])) </pre>

pyrexdraum on Dec. 17, 2021, 5:56 a.m.
Genius!

sakshamjswl45 on March 24, 2022, 4 a.m.
where does the i come from?

jakubbortlik on Nov. 28, 2022, 7:12 a.m.
The `i` is assigned here: `i := s.rfind('.')` - this is the "walrus" from the solution title, or the assignement expression which evaluates to a value and is assigned to the variable before `:=` at the same time. <a href="https://realpython.com/python-walrus-operator/">This article</a> provides a nice description.

oleg.sidorov.ds on Sept. 2, 2023, 1:31 p.m.
Sorting order: files without name, files without extension, files with name and extension; Filename ".config" or "config." is all name with an empty extension; Ok... <ul> <li>".config" – empty extension (second priority)</li> <li>".www" – empty name (first priority)</li> </ul> This solution gives: `sortbyext(['.config', '.www'])` `['.config', '.www']` – that's wrong result

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