Shortest Python Quine?

Shortest Python Quine?

by Sean B. Palmer

This morning I scribbled down, pen on paper, a Python Quine. I hadn't actively looked into Quine techniques before; it was nice to start from scratch. Here's what I got, with a little reduction when I typed it up (my scribbled version had used a function instead of lambda):-

print (lambda s:s+`s`+')')("print (lambda s:s+`s`+')')(")

At this point, I went searching for the shortest Python Quine that anyone had come up with. I found Seth Schoen's challenge again, though it doesn't actually contain the code for the Quine that he came up with. Searching elsewhere, I found a couple of sites (The Quines List, The Quine Page) that had basically the same Quine (one credited to Manus Hand, the other to Frank Stajano):-

_='_=%s;print _%%`_`';print _%`_`

It was shorter than mine (since it assigns first and then prints), but I noticed that it could easily be made shorter still. So here I present what might just be the shortest possible non-empty Python Quine, at thirty characters:-

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

It seems odd that the original authors didn't use %r in the first place (perhaps they were going by a version of Python that didn't have %r; when was it added?). For total authenticity, you should include a line break after it. Putting a comma after each %_ would stop the line break, but make it two characters longer, and therefore longer overall by one character.

As for my print-first approach, I managed to shorten it to the following:-

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

Which is fairly respectible, at fifty-two characters.

I wonder what the shortest possible multi-quine is? (Check out David Madore's investigation into Quines for a definition.) Also, I wonder if it's possible to prove that a Quine in a given langauge is the shortest possible for that language, other than by using the evidence that no-one has come up with a shorter one yet? Feedback most welcome.