Get to the point! clear solution for Sort by Extension by veky - python coding challenges

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Get to the point! solution in Clear category for Sort by Extension by veky

def extension_then_stem(filename):
    try: point = filename.rindex('.', 1)
    except ValueError: point = len(filename)
    return filename[point:], filename[:point]

from functools import partial
sort_by_ext = partial(sorted, key=extension_then_stem)

July 15, 2020

Comments:

PetrStar on Nov. 26, 2020, 9:52 p.m.
you can use rfind (without try except)

veky on Dec. 3, 2020, 6:03 a.m.
Of course I can, but why would I want to do that? I'd still have an exceptional case, only it would be encoded "in band" as a special return value. To me, except captures the intent much better than a generic if towards a returned number: -1 is quite arbitrary from the point of Python.

romich95 on Dec. 11, 2020, 11:16 p.m.
Understood nothing, but very interesting🤔

veky on Dec. 12, 2020, 4:57 a.m.
Seriously, did you not understand e.g. the first line? :-P But nevermind. The important question is: do you want to understand?

santosleonardo707 on Feb. 6, 2021, 4:13 a.m.
I love that you always try and teach something with your solutions. I see what you did there: <pre class='brush: python'>def sort_by_ext(files): return sorted(files, key=extension_then_stem) # boring. Nothing new to learn </pre> You're inspiring! I appreciate your hard word!

veky on Feb. 6, 2021, 7:16 a.m.
Thanks for recognizing that. :-)

veky on June 4, 2021, 10:42 a.m.
BTW you're wrong. Many people would write an even more complicated <pre class='brush: python'>sorted(files, key = lambda filename: extension_then_stem(filename)) </pre> ;-)

Janoo12 on Oct. 31, 2022, 10:01 p.m.
I need to write a codereview for quest points so I write down how I figured out what your code actually means. except ValueError: point = len(filename) - this is the case if the filename starts with a point and there is no other point so basically the no stem case. In this case the filename[point:] is an empty string and the first item of the tuple based on which the sorting happens so these cases will be the first ones. If there is no extension, the point will point to the last character's index so the first item of the tuple will be a '.', the second will be the stem. If there is both stem and extension then the first item of the tuple will contain a point and the extension which is more than a single '.' so these cases only come after the previous only stem case. The partial part simply defaults the sorted function's key argument to the freshly created extensionthenstem function. The thing that I like the most in this solution is the fact that the final expression doesn't even hold the input parameter - filenames.

veky on Nov. 1, 2022, 1:05 a.m.
<blockquote> case if the filename starts with a point and there is no other point </blockquote> Of course, there could also be no point at all. <blockquote> final expression doesn’t even hold the input parameter </blockquote> Nor does it have to: sorted doesn't care how its argument is named. <pre class='brush: python'>sorted(iterable, /, *, key=None, reverse=False) </pre> See that `/`? It means first argument is strictly positional.

fenthick88 on April 26, 2024, 12:18 p.m.
Great solution, except for unpythonic code formatting.

veky on April 26, 2024, 7:27 p.m.
You mean lines 2 and 3, or something else?

fenthick88 on April 27, 2024, 10:25 a.m.
Pylint output below as a reference. <pre class='brush: python'>:2:9: C0321: More than one statement on a single line (multiple-statements) :3:23: C0321: More than one statement on a single line (multiple-statements) :6:0: C0413: Import "from functools import partial" should be placed at the top of the module (wrong-import-position) </pre>

veky on April 28, 2024, 12:36 p.m.
First, no tool can determine how pythonic some code is. You're probably aware of pycodestyle's battles with PSF. "More than one statement on a single line" is wrong, at least if you think about two statements side by side. Assignment to `point` is a statement, and it is in fact the only statement in line 2 (an also the only statement in line 3). "try:" by iself is not a statement, same as "except ValueError:" by itself. Import placement I wouldn't call "formatting"... the idea probably stems from PEP8, which is reasonable for the code in Python stdlib (for which PEP8 is written), but is usually too bureaucratic for small functions such as this one. (I'd really like to know whether pylint also enforces the "three groups of imports with a single line between them" which PEP8 also prescribes. My guess is that it doesn't, because almost nobody writes code like that.) I'm not importing partial in order to use it at many places in the code (in that case a top-level import would be prudent)... I'm using it only to construct the function that CheckiO testing system needs. In real life code, I probably wouldn't use partial at all, I'd just call `sorted` with that `key` directly.

fenthick88 on April 28, 2024, 2:10 p.m.
First of all, thanks for the comprehensive answer. Unfortunately, I can't agree with some of your points. Find 'try statement' on page <a href="https://docs.python.org/3/tutorial/errors.html.">https://docs.python.org/3/tutorial/errors.html.</a> There are nine results, try clause with only some expression inside will still be a statement, so in your code, the assignment is a second statement. I doubt there is a place in the whole pydocs where you will see such one-liners. When it comes to import ... from, there are good arguments why it should be at the top of it. Of course, it's not that important in this context, but as you know, the module's namespace is populated with a 'partial' object no matter where you do it globally. It may be used in the first function as well. Results will be different depending only on where it's called.

veky on April 28, 2024, 5:20 p.m.
No problem; we're both here to learn. I'm really not sure how you read from that docs that you mentioned, that a "try clause" will still be a statement. I think the docs are trying [pun] really hard not to convey that notion. Try (compound) statement consists of many clauses: try clause, except clauses, else clause and finally clause. There are various constraints regarding the number of each of them in a single statement, but still, it's quite obvious that all of it is just one statement. Example: <blockquote> If a finally clause is present, the finally clause will execute as the last task before the try statement completes. </blockquote> It would really be incorrect if "try statement" could be understood as just "try clause" here. <hr /> Yes, there are good arguments, and none of them apply here. ;) In particular, no, the results wouldn't be different if `partial` was used in the first function as well. If you don't believe me, you're welcome to try.

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