Hinted clear solution for Number Base by veky - python coding challenges

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Hinted solution in Clear category for Number Base by veky

def checkio(*a):
    try: return int(*a)
    except ValueError: return -1

Feb. 20, 2014

Comments:

nickie on Feb. 20, 2014, 8:42 p.m.
(+1) for the "*a"... :-)

veky on Feb. 20, 2014, 9:15 p.m.
You mean -1 (chars)... ;-)

sudharshan.adroit on Oct. 1, 2015, 11:32 p.m.
Doesn't *a allow the caller to pass invalid number of args??

veky on Oct. 2, 2015, 4:58 a.m.
Of course. And then you'll get a TypeError. Same as you would get if there was no `*`. Even better, the TypeError will point to the right function that doesn't handle e.g. three arguments, and that is `int`. Even better, if some day Guido adds third argument to `int`, it will magically just work here. Try to understand, Python is a "consenting adults" language, not "bondage and discipline" language. It has disadvantages, but it has many advantages too. (BTW that's why empty excepts are horrible. If I just wrote "except:" in line 3, then function would return -1 in that case, and your objection would stand.)

Cjkjvfnby on March 1, 2014, 11:59 p.m.
Exact as I expect.

veky on March 2, 2014, 6:26 a.m.
I'm becoming predictable. :-D

Cjkjvfnby on March 2, 2014, 12:09 p.m.
You have you own programming style :)

exspecto_9defa3dd6bc7474683100 on Nov. 27, 2015, 3:58 a.m.
As proof, when I solved this, I first thought "What would veky do?" and immediately used try/except.

veky on Nov. 27, 2015, 4:10 a.m.
Ah, WWVD... the surest sign I'm becoming a pillar of morality. :-DD

vonauer on March 22, 2014, 10:48 a.m.
That's brilliant! :-)

lucas.bertola on April 6, 2014, 9:12 p.m.
Nice :)

kamikaze on April 17, 2014, 12:42 p.m.
nice. but while you are trying to reduce line count you are violation PEP-8 and readability :)

veky on April 17, 2014, 1:53 p.m.
Without your comment, I never would have realized that. :-P

Cjkjvfnby on April 17, 2014, 2:05 p.m.
Little strokes fell great oaks.

veky on April 17, 2014, 3:30 p.m.
I'm more of a Tacoma bridge. ;-D

codeM0nk3y on June 29, 2014, 3:57 a.m.
This may be a brilliant solution, but it is not clear in the least.

veky on June 29, 2014, 5:34 a.m.
I'm sorry for that. What do you find unclear?

codeM0nk3y on June 30, 2014, 2:28 a.m.
Maybe it's just a newbie thing, but changing the parameters to *a was confusing to me.

veky on June 30, 2014, 3:36 a.m.
It's a standard thing in Python when writing a thin wrapper for another function (usually to handle some exceptions, just like here). What I called "*a" here is usually called "*args" in such schemes, and it's also usually put together with "**kw" for absolute generality, here unneeded. Also people frequently use @functools.wraps decorator for preserving function metadata like name and docstring (here also unnecessary, I'd say). It just means: however you're called, delegate your work to int, and convert its possible ValueError to return of -1. Such schemes usually trip up newbies who think that every argument must have a separate name, but they are pretty standard. You can find canonical example <a href="https://docs.python.org/3.5/library/functools.html?highlight=wraps#functools.wraps">here</a>.

taras-sereda on Aug. 12, 2014, 8:38 a.m.
Thanks for your explanation. Now it's clear. I'm curios why *args version works 2 times faster than this implementation? May be you can point where I can read about this topic. Thanks! <pre class='brush: python'>def checkio(str_number, radix): try: return int (str_number, base=radix) except ValueError: return -1 </pre> 1000000 loops, best of 3: 973 ns per loop 1000000 loops, best of 3: 403 ns per loop

veky on Aug. 12, 2014, 10:35 a.m.
Well, your version has to unpack the args into str_number and radix, an operation which is not really expensive, but since the whole program is just a wrapper around builtin int, it happens to make a difference.

taras-sereda on Aug. 12, 2014, 11:19 a.m.
thanks. In essence it's not the matter of time execution. It's more for understanding what leads to this difference.

TheBmo on Aug. 11, 2014, 8:34 p.m.
Thanks for explaining that. I had the same answer as you, minus the arguments which was a great idea. Tripped me up at first but your explanation was very helpful.

veky on Aug. 11, 2014, 10:14 p.m.
<blockquote> I had the same answer as you, minus the arguments </blockquote> Exactly why I wrote it. I want to teach people something, there's no point in all of us having the same solution. ;-)

codeM0nk3y on June 30, 2014, 2:28 a.m.
Maybe it's just a newbie thing, but changing the parameters to *a was confusing to me.

tdietert on July 1, 2014, 4:48 p.m.
true knowledge of python! Thanks for teaching me a simple work around to the long function I wrote!

veky on July 1, 2014, 5:21 p.m.
I'm always happy to do that. ;-)

pynur on Oct. 18, 2014, 2:46 p.m.
Ha-ha!!! You can't use here lambda, ha!!!

veky on Oct. 18, 2014, 8:14 p.m.
First and most important, why would I? You should use the right tool for the job. When the job is inbanding exceptions, stackframe is in order. It might come as a surprise, but I'm not trying to solve everything with lambda. I'm just trying to solve everything that can be best solved with lambda, with lambda. :-) And secondly, maybe I cannot (a priori), but <a href="http://www.checkio.org/forum/post/1485/vekyization-challenge/#comment-8576">htamas can</a>. Don't think something is impossible just because you (or even I:) can't seem to think of a way. ;-P

ahmedaswai on Nov. 1, 2014, 5:19 p.m.
Are you series , I feel my self dumb now

veky on Nov. 1, 2014, 7:15 p.m.
Sorry about that... is there anything I can do to help you? Have you read other comments?

Freiling on July 3, 2017, 10:35 p.m.
This one was tricky. Far simpler than the ones before it, very inviting to overthinking. I never would have guessed at first that we're basically just repackaging a built-in function.

veky on July 4, 2017, 4:41 a.m.
Ah, you wouldn't believe how many "missions" people conceive are just a repackaging of a function Python already has. It usually goes like this: oduvan posts "hey, I have a new mission, check it out!". I post <pre class='brush: python'>from some_obscure_stdlib_corner import same_functionality as checkio </pre> and then he usually goes back to the drawing board. :-D

Timon666 on Nov. 22, 2014, 9:13 p.m.
lol being completely new in Python didn't know about that there's such a nice method)) I wrote method by myself ;-) Thanks for opening my eyes

veky on Nov. 23, 2014, 6:34 p.m.
"Batteries included", remember? Whenever you try to write something you're sure somebody needed before, stop. And search standard library. :-)

Timon666 on Nov. 24, 2014, 9 p.m.
Yeap, these days do it almost all the time ;)

Fedorovich on Dec. 16, 2014, 2:58 p.m.
Why write? <pre class='brush: python'>except ValueError: return -1 </pre> It is to work too. <pre class='brush: python'>except: return -1 </pre>

veky on Dec. 16, 2014, 3:27 p.m.
Yes, it "works". And then you write something a bit bigger, and it executes too long, and you press Ctrl+C to stop it. But it doesn't stop, it returns -1. :-F Or, you mistakenly write strnubmer instead of strnumber. Python doesn't report an error, your code "works" and always returns -1. :-F Or, you confuse order of arguments and call int(radix, str_number) (e.g. Mathematica puts base first). Your function returns -1. :-Fail You see? Masking exceptions is never a good idea, and it's twice ungood idea in a dynamic language such as Python.

Fedorovich on Dec. 17, 2014, 7 a.m.
Thank you.

petrch on Jan. 5, 2015, 10:17 p.m.
Oh, I read the *a tip in some of your previous solutions and I already forget it again.

veky on Jan. 5, 2015, 10:51 p.m.
Use it and you won't forget. ;-)

mscmorris on Feb. 6, 2015, 4:44 p.m.
Very nice. This is what I came up with except I'm new to Python and didn't know you could use arguments in such a way. Thanks for the learning moment!

veky on Feb. 6, 2015, 4:47 p.m.
No problem. Learning moments is why I'm here. :-)

gnucian on June 21, 2015, 8:24 a.m.
Looking at your solution, I felt like I had reinvented the wheel. :-<

veky on June 21, 2015, 12:05 p.m.
Happens to many people. My memory is very associative, I know all Python documentation by heart, and I often think about a problem for a day before I sit and write a simple solution. :-)

yersen on July 19, 2015, 2:38 p.m.
Really great!!!

veky on July 19, 2015, 7:09 p.m.
Thanks.

KateQuark on July 30, 2015, 1:16 p.m.
I learn new stuff in Python just from your solutions.. Thanks for that

veky on July 30, 2015, 8:54 p.m.
That's the reason I write them. :-)

PyPoet on Sept. 16, 2015, 3:22 a.m.
Nice trick to save characters.

veky on Sept. 16, 2015, 8:53 a.m.
What concrete characters do you think I've saved? As I said above, `*` is idiomatic when delegating functions. But if you meant that `a` should have been `args`, you're probably right.

PyPoet on Sept. 16, 2015, 1:53 p.m.
I was referring to the comma between the two expected arguments. Actually I didn't really notice the 'missing' rgs...

veky on Sept. 16, 2015, 2:02 p.m.
You could say that the side effect was to save the comma. But when f says "just call g with whatever arguments you get, and then do something else", it's idiomatic to use args (and *kwargs if you need to also handle keyword arguments). It was a teaching moment, and you could say it is a trick, but it surely wasn't primarily to save characters.

PyPoet on Sept. 16, 2015, 3:43 p.m.
much appreciated

TomaszPecyna_65a0f3bb2a6947878 on Oct. 23, 2015, 10:25 a.m.
awesome solution

veky on Oct. 23, 2015, 10:48 a.m.
Thanks. :-)

M157q on Nov. 5, 2015, 3:29 p.m.
nice `*a` lol

veky on Nov. 6, 2015, 4:32 a.m.
You can laugh, but you can also <a href="http://www.checkio.org/mission/number-radix/publications/veky/python-3/hinted/share/8da2e6d92d35d3efa165fc7617073cbc/#comment-14770">learn something</a>. ;-)

marceelofernandes on May 2, 2016, 8:02 a.m.
1 year programming in python and i never had a chance to face this *a, now i understand it... Thanks man, you did a good job right there!

ljy95135 on May 25, 2016, 7:46 a.m.
I used to think we must use the original parameter to get passed. It gives me new knowledge, brilliant. :)

veky on May 25, 2016, 10:17 a.m.
As I told you in another comment, all CiO wants is (in the true ducktyping manner) something it can call with two arguments, and get an int (or something that quacks like it) back. You could even do <pre class='brush: python'>class checkio(int): def __new__(*args): try: return int.__new__(*args) except ValueError: return -1 </pre> But don't say I told you that. ;-D

ljy95135 on May 25, 2016, 10:20 a.m.
cool! CiO can even be a class :)

veky on May 25, 2016, 10:41 a.m.
It can be anything callable (returning an int-like thing). Look: <pre class='brush: python'>class Bandersnatch: def __call__(self, *args): try: return int(*args) except ValueError: return -1 checkio = Bandersnatch() print(type(checkio)) </pre> Now checkio is a bandersnatch. :-D The whole point of duck typing is that you aren't obsessed with what things are, but how they behave.

ljy95135 on May 25, 2016, 10:46 a.m.
amazing! I get your meaning now, it's like a lambda function give to checkio, and as long as it's legal for test, it will be passed. Thank you, it's very helpful for me :-D

veky on May 25, 2016, 10:55 a.m.
Yes. You'll notice that the "essence" of a solution, try/except lines, are getting drowned in increasingly more and more boilerplate. It's natural to ask how to minimize it, so the essence really shines (the alternative strategy is to blow up the essence to 60 lines, which I've also seen people do here;)). In other words, what's the simplest boilerplate that could possibly work? And usually, it's a lambda. (Here it isn't, since you need statements to handle exceptions normally, and philosophically, a stack frame corresponds to a function call anyway - so here a `def' is the answer).

Alexandr_Zhytenko on March 9, 2017, 2:40 p.m.
excellent

WillofD_6cb47ad155eb4e6497f96c on April 3, 2017, 6:35 a.m.
impressive!

ghostishev on April 19, 2017, 10:43 a.m.
Nice solution!

chris.porter.413 on April 30, 2017, 1:37 a.m.
This is elegant.

ouhuazheng on July 7, 2018, 1:40 a.m.
Cool! Didn't know int() could have a second argument... So I wrote many lines, maybe I should review most of the built-in functions ：）

veky on July 9, 2018, 7:30 a.m.
Yup. For builtin functions you'll be surprised have a second argument, try `iter`. :-D Also `eval`/`exec`, but not so impressive. And `next`, though you probably already knew that. Oh yeah, `property`. It takes a lot of optional arguments. But when you understand a second argument to `super`, you can say you get Python. :-]

dandd31 on July 25, 2018, 1:50 a.m.
Nice

hugoboss on Aug. 9, 2018, 12:15 p.m.
Yes, I'll milk you dry:) *args and one-line try\else condition + result make life easy! I just love your style.

veky on Aug. 10, 2018, 2:02 a.m.
Go forth, I have enough milk. :-P As I said above, the function is a thin wrapper around `int`. Simple is better than complex. ;-)

Magu on Oct. 14, 2023, 6:55 a.m.
Wow. It's elegant. An impressive solution. :D

asapfrogy on Oct. 16, 2023, 4:26 p.m.
great

gleb10101010101 on Jan. 12, 2024, 11:36 a.m.
Great! I was trying to solve this mission with a minimum number of letters, but my solution is at least three times longer then this...

veky on Jan. 12, 2024, 9:10 p.m.
well, most of the reason is that you left all the asserts in. :-)

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