Shortest Python Quine?

Question

Python 2.x (30 bytes):

_='_=%r;print _%%_';print _%_

Python 3.x (32 bytes)

_='_=%r;print(_%%_)';print(_%_)

Is this the shortest possible Python quine, or can it be done better? This one seems to improve on all the entries on The Quine Page.

I'm not counting the trivial 'empty' program.

"can it be done better?" Although this question has definitively an answer it is hard to be answered (unless the answer is yes and you have a counterexample). How should someone know without testing ALL possible shorter programs? — Howard, Jun 03 '11 at 05:27
@Howard: At some point, there aren't all that many of those... — Nemo, Jun 03 '11 at 05:32
well, since we're down to <30 characters, and there's a finite symbol set for the syntax, a proof may even be possible by enumeration? but i was more thinking someone might be able to chime in with "I can do better!" after all, this quine is only a slight modification of Frank Stajano's idea from the quine page.. ;) — wim, Jun 03 '11 at 05:32
@Michael Foukarakis : awww :( what broke it in python 3? new print function? — wim, Jun 03 '11 at 06:01
Yes, `print` is a function in 3.x, making parentheses mandatory. — Michael Foukarakis, Jun 03 '11 at 06:10
For the record, `_='_=%r;print(_%%_)';print(_%_)` works in python3. — Mechanical snail, Jul 12 '11 at 02:28
I'd prefer to write it as `r='r=%r;print r%%r';print r%r` (for python2), though. — Mechanical snail, Jul 12 '11 at 02:53
"[A quine is ***a non-empty computer program*** which takes no input and produces a copy of its own source code as its only output.](https://en.wikipedia.org/wiki/Quine_(computing))". So, an 'empty' program isn't a Quine. — YaOzI, Mar 20 '16 at 08:55
The shortest quine is 1 byte shorter than this actually, on code.golf — DialFrost, Jan 05 '23 at 23:18
@DialFrost Interesting, you're right - the top submissions [there](https://code.golf/quine#python) are 31 bytes. I wonder what that is (I can't see the solutions) — wim, Jan 06 '23 at 02:18

score 72 · Answer 1 · answered Jul 30 '15 at 12:52

72

I'm just going to leave this here (save as exceptionQuine.py):

    File "exceptionQuine.py", line 1
        File "exceptionQuine.py", line 1
        ^
IndentationError: unexpected indent

answered Jul 30 '15 at 12:52

Beurtschipper

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Why do you have to save as exceptionQuine.py? The error output is the code regardless of the filename, no? – Quinn Culver Jan 23 '16 at 00:49
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No. Let's say I save the file as foo.py, the output will be: `File "foo.py", line 1 File "exceptionQuine.py", line 1 ^` – Beurtschipper Jan 24 '16 at 02:09
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Very clever. However I'm not sure that stderr is counted as output :-) Also, are you being a little jocular with your reply to Quinn regarding the filename? – Matthew Hannigan Jan 28 '16 at 08:25
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I don't care what anyone says, this answer is the single best one. – BlackCoffee Sep 09 '20 at 04:35
How is this shorter than the example provided by the asker? – flarn2006 Sep 04 '21 at 03:05

Mechanical snail · Answer 2 · 2012-09-25T01:10:09.137

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Technically, the shortest Python quine is the empty file. Apart from this trivial case:

Since Python's print automatically appends a newline, the quine is actually _='_=%r;print _%%_';print _%_\n (where \n represents a single newline character in the file).

edited Sep 25 '12 at 01:10

answered Jul 12 '11 at 02:52

Mechanical snail

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hmm, you are right. alternatively , perhaps the new line can be suppressed like `r='r=%r;print r%%r,';print r%r,` – wim Jul 12 '11 at 03:18
That would be 1 character longer, and it wouldn't work in python3. – Mechanical snail Jul 12 '11 at 18:48
@wim: 1 character (on Linux). – Mechanical snail Jul 13 '11 at 04:22
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@wim: I mean there should be an actual newline in the file, but stackoverflow doesn't make it easy to write. – Mechanical snail Jul 13 '11 at 08:18
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I don't think "Technically, the shortest Python quine is the ***empty file***.". Because: "[A quine is **a non-empty computer program** which takes no input and produces a copy of its own source code as its only output.](https://en.wikipedia.org/wiki/Quine_(computing))". – YaOzI Mar 20 '16 at 08:51

score 14 · Answer 3 · answered Oct 30 '13 at 04:52

14

Both

print open(__file__).read()

and anything involving import are not valid quines, because a quine by definition cannot take any input. Reading an external file is considered taking input, and thus a quine cannot read a file -- including itself.

For the record, technically speaking, the shortest possible quine in python is a blank file, but that is sort of cheating too.

answered Oct 30 '13 at 04:52

wintermute

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"For the record, technically speaking, the shortest possible quine in python is a blank file, but that is **sort of cheating** too." Correction: it **is** cheating. – EKons Apr 14 '16 at 13:51

postylem · Answer 4 · 2017-07-17T14:28:20.453

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In a slightly non-literal approach, taking 'shortest' to mean short in terms of the number of statements as well as just the character count, I have one here that doesn't include any semicolons.

print(lambda x:x+str((x,)))('print(lambda x:x+str((x,)))',)

In my mind this contends, because it's all one function, whereas others are multiple. Does anyone have a shorter one like this?

Edit: User flornquake made the following improvement (backticks for repr() to replace str() and shave off 6 characters):

print(lambda x:x+`(x,)`)('print(lambda x:x+`(x,)`)',)

edited Jul 17 '17 at 14:28

answered Sep 12 '14 at 12:04

postylem

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[This comment](/questions/6223285/#comment7249082_6223285) explains the OP's interest for small size in bytes. – EKons Apr 19 '16 at 14:54
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This one is my favorite! – Elliot Gorokhovsky Dec 25 '16 at 05:44
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Note that backticks are `repr`, not `str`. – CalculatorFeline May 28 '17 at 05:16
Thanks @CalculatorFeline. I edited it to incorporate that tidbit. – postylem Jul 17 '17 at 14:29
5

Nice! Here's Python 3.6 with f-strings: `print((lambda x:f"{x}{x,})")('print((lambda x:f"{x}{x,})")',))` – Feb 28 '18 at 01:35

OlivierBlanvillain · Answer 5 · 2013-08-29T21:33:44.510

11

Even shorter:

print(__file__[:-3])

And name the file print(__file__[:-3]).py (Source)

Edit: actually,

print(__file__)

named print(__file__) works too.

edited Aug 29 '13 at 21:33

answered Aug 29 '13 at 21:14

OlivierBlanvillain

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Nice abuse of the rules ;) – Tino Feb 22 '15 at 04:40
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upvote, it's good :) I can't help but feel quine program is nicer if it works independently of the filename though – wim Feb 18 '16 at 03:45
This cheat works with `gcc`, too (following needs `bash`): `a=$'main(){write(1,__FILE__,29);}'; echo -n "$a" > "$a.c"; gcc "$a.c"; ./a.out | cmp - "$a.c"; echo $?` (note, this does not contain any linebreaks) – Tino Dec 20 '16 at 17:38
15 bytes+15 bytes for filename=30 bytes by PPCG scoring. Not quite good enough. – CalculatorFeline May 28 '17 at 05:18

RaminNietzsche · Answer 6 · 2020-04-01T00:11:10.697

7

Python 3.8

exec(s:='print("exec(s:=%r)"%s)')

edited Apr 01 '20 at 00:11

answered Mar 29 '20 at 21:57

RaminNietzsche

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It's invalid: [*Quines, per definition, cannot receive any form of input, including reading a file, which means a quine is considered to be "cheating" if it looks at its own source code.*](https://en.wikipedia.org/wiki/Quine_(computing)) – wim Mar 29 '20 at 22:15
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But I thought something like `print open(__file__).read()` is invalid. :D thanks for information – RaminNietzsche Mar 30 '20 at 07:16
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Yep, I guess that one is invalid too (as other commenters already pointed out) – wim Mar 30 '20 at 07:17
@wim I change it ;) – RaminNietzsche Apr 01 '20 at 00:11
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`print((_:='print((_:=%r)%%_)')%_)` – Marcus Weinberger Sep 29 '20 at 19:35

score 6 · Answer 7 · answered Mar 02 '19 at 15:43

6

Here is another similar to postylem's answer.

Python 3.6:

print((lambda s:s%s)('print((lambda s:s%%s)(%r))'))

Python 2.7:

print(lambda s:s%s)('print(lambda s:s%%s)(%r)')

answered Mar 02 '19 at 15:43

Tim

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ah yes, a little nicer than mine perhaps. – postylem Jul 02 '19 at 16:37

score 3 · Answer 8 · answered Sep 29 '20 at 19:31

As of Python 3.8 I have a new quine! I'm quite proud of it because until now I have never created my own. I drew inspiration from _='_=%r;print(_%%_)';print(_%_), but made it into a single function (with only 2 more characters). It uses the new walrus operator.

print((_:='print((_:=%r)%%_)')%_)

manojlds · Answer 9 · 2011-06-03T05:38:32.873

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I would say:

print open(__file__).read()

Source

edited Jun 03 '11 at 05:38

answered Jun 03 '11 at 05:30

manojlds

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That's not really in the spirit of the question. – Nick ODell Jun 03 '11 at 05:34
Oh, and if you put backslashes before the parens, the link in your post won't be broken. – Nick ODell Jun 03 '11 at 05:37
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That breaks the rules of quines. A quine is a program that writes its own source as an output *without reading it the original source file*. – panzi Jul 02 '14 at 01:44
Where are the rules of quines? Can you find a set of rules for quines that does not include that rule? – Noctis Skytower Aug 26 '14 at 21:20
Can you find a set of rules for quines that include themselves? – André Laszlo Mar 12 '15 at 11:13
Why is there so much rage in the comments without an explanation? The correct form of commenting for breaking the rules should explain the no I/O rule is being broken. – EKons Apr 19 '16 at 14:56

score 0 · Answer 10 · answered Apr 07 '21 at 12:31

0

This one is least cryptic, cor is a.format(a) a="a={1}{0}{1};print(a.format(a,chr(34)))";print(a.format(a,chr(34)))

answered Apr 07 '21 at 12:31

miroB

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Tino · Answer 11 · 2013-09-16T15:43:01.267

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I am strictly against your solution.

The formatting prarameter % is definitively a too advanced high level language function. If such constructs are allowed, I would say, that import must be allowed as well. Then I can construct a shorter Quine by introducing some other high level language construct (which, BTW is much less powerful than the % function, so it is less advanced):

Here is a Unix shell script creating such a quine.py file and checking it really works:

echo 'import x' > quine.py
echo "print 'import x'" > x.py
python quine.py | cmp - quine.py; echo $?

outputs 0

Yes, that's cheating, like using %. Sorry.

edited Sep 16 '13 at 15:43

answered Sep 16 '13 at 15:28

Tino

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`%` is just a language function, like concatenation or multi-line strings. Using external resources (like an extra file that's not included in the quine) is plain cheating. – BoppreH Oct 24 '13 at 01:21
Actually, `import` is just a language function, like concatenation or multi-line strings. Using external ressources (like using `#include ` in C or linking the standard library) is perfectly valid in quines (else there would be no quines in compiled languages). However there is a good cause why not to allow too advanced high level functions in a language, like languages allowing introspection (and there are introspection modules for Python readily available). Hence what I wrote: The consequence from outlawing `import` is to outlaw `%`, too. Sorry folks! – Tino Dec 07 '13 at 16:22
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Do you outlaw %s in C quines, too? – Patrick Collins Apr 20 '14 at 04:18
I definitively call it cheating. `printf` is a high level library function, not a basic language construct. If you implement something like `printf` in your quine that is ok. But abstain from higher level library functions, only use basic I/O, please! – Tino Apr 21 '14 at 00:58
Adding one thing: The only thing where the use of the `printf` function could be acceptable in C Quines is for the (exact!) usage `printf("%s",s)` in situations, where `printf(s)` might abuse the formatting function of `printf`. Compare `f=printf;o="%s";f(o,s)` saves 1 byte compared to `f=fputs;o=stdout;f(s,o)`. I would call this the only possibly legitimate use of `printf` (or `%s`) in C Quines. There might be similar uses of `%` in Python, but I don't think those constructs are shorter than the direct output. – Tino Apr 21 '14 at 01:29
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As far as I am aware, the purpose of a quine is to write a program that outputs its own source without external inputs. % does not use an external source. Import can be viewed in two ways. Either you consider the second file an external source (thus breaking the rules) or you consider the imported code as part of the source, in which case your quine does not print out the "full source". Thus % does not violate quine rules, and your import does. – vastlysuperiorman Feb 20 '15 at 01:12
@vastlysuperiorman: `touch nix.py; python nix.py | cmp nix.py -`. However `nix.py` (the empty file) is no quine. Read: With quines, it's simply is not that simple as you probably think. Also: import does not use external sources, as this is compile time, not runtime. – Tino Feb 22 '15 at 04:28
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@Tino You "outlawed" `import` statements [here](/questions/6223285#comment30541410_18831770) – EKons Apr 19 '16 at 15:04
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@ΈρικΚωνσταντόπουλος If you agree to my statement there, you also agree, that `%` is cheating!?! As my argument is: `%` is cheating, iff `import` is cheating. This means, either we allow both, or none. And again, I repeat: `import` is not accessing external resources like `#include ` isn't cheating and linking in standard C libraries isn't, too. Only using too high level functions is cheating! And my argument is, that `import` is even a lower level construct than `%`! So using any is cheating. BTW: Why am I downvoted while http://stackoverflow.com/a/18521084 is upvoted? – Tino Dec 20 '16 at 17:13
@Tino Please cool down a bit. `%r` is just 2 characters of the string. The operator `%` that uses them is just an operator, not an external thing. The `repr` builtin is also a builtin, not a high-level function. – EKons Dec 20 '16 at 17:34
@ΈρικΚωνσταντόπουλος Thanks for noting this! Until now I focused entirely on `print _%_` being something like `printf(a, a)` which usually is considered cheating in C quines. I fully oversaw this `%r` which is even worse! It uses `repr()`, which is language introspection. Do you really think, language introspection shall be allowed in quines? – Tino Dec 20 '16 at 18:09
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@Tino I can't seem to understand you I guess. Also, why shouldn't it be allowed? It's just that you can't read input and you can't have an empty program. – EKons Dec 20 '16 at 18:12
@ΈρικΚωνσταντόπουλος Sorry, I meant [Reflection](https://en.wikipedia.org/wiki/Reflection_(computer_programming)). Reflection allows a program to look at its own source code. [This commonly is considered cheating in quines.](https://en.wikipedia.org/wiki/Quine_(computing)#.22Cheating.22_quines) Please note that we are at 13 comments for 13 downvotes now. So I thank you very much to reach the recommendation for ["a comment per downvote"](http://meta.stackexchange.com/a/2373) without need for spam. I'll now stop commenting until the need for comments arises again. Merry Xmas! – Tino Dec 20 '16 at 18:48
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[PPCG has a good definition of quines](https://codegolf.meta.stackexchange.com/questions/4877/what-counts-as-a-proper-quine).`repr()` does _not_ use reflection. It is a standard function that takes string inputs and outputs other strings. An example would be does `repr(input())` read the source at all? The string just happens to include part of the source, as the source defines the string (As what else would when hard-coding a string?). And `%` on a string is just string formatting. Formatting is also a function that doesn't rely on the source, just the arguments (i.e. no side effects.) – Artyer Jun 02 '17 at 19:26
Saying `%` is invalid is like saying recursion is invalid. `%` accesses a string, not the program itself. Recursion accesses a function, not the program (however, recursion would be invalid for function quines) – MilkyWay90 Mar 02 '19 at 16:35

Shortest Python Quine?

11 Answers11

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