Here's a Ruby analog in 60 lines with added support of continuations (call/cc, famous Scheme feature):
http://stuff.thedeemon.com/ris...
Requires Ruby 1.8.x.

Oh My Gawd. I searched for 'how to write simple language interpreters in python' and reached this page(thank you google). This article had two profound impacts on me. 1) I understood how to write lisp interpreters in python(obvious) and 2) I understood LISP for the first time. For atleast two years I have gone on and off about Lisp, never really 'getting' it. Always thought it was a lousy language no matter how much people loved it. That thought changed after this article. It has embarked me onto writing my own lisp dialect(not again) and also learning Lisp with a new attitude. Now I think of only one thing, I wish Python had equivalent of (defmacro) of lisp. :-) Thanks Mr. Norvig - I will buy your book on Artificial Intelligence to (somehow) support this webpage :-D.

Chapter 11 of this book http://www.computingbook.org/ [http://www.computingbook.org/I...] is all about a Python implementation of a mini-Scheme interpreter.  (This problem set, http://www.cs.virginia.edu/~ev..., is about extending that interpreter).

Here is a version of this in Javascript. I created this so that I could run through the examples/exercises in SICP while commuting.
https://bitbucket.org/sainamda...

I was going over this to present it in a class and noticed that there is no variable bound to the empty list. We can use (quote ()) for the the empty list, as in (define x (cons 1 (cons 2 (quote ())))), but the way lists work in Python, (eq? (quote ()) (quote ())) is False. So I think it would be good to pre-define a global variable null initially bound to []: global_env['null'] = []

Very nice and inspiring!
FYI there is a nice small lisp implementation in C from Piumatra (a researcher with Alan Kay at VPRI)
at http://piumarta.com/software/l...

Very sweet. But you know, what would really be interesting would be to see how many lines of code you need to do this in something that doesn't have built-in recursion and in which you have to describe garbage collection. Something like an assembly language...

there's a missing closing paren in below example

>> program = "(define area (lambda (r) (* 3.141592653 (* r r)))"

it should be

>> program = "(define area (lambda (r) (* 3.141592653 (* r r))))"

Hi Peter
I am studying interpreters and compilers recently. Reading this article helps me a lot. I think this might also help other CS students in Taiwan so that I translate it into Traditional Chinese. If you mind, please let me know and I will remove the post.
http://reborn2266.blogspot.com...

Thanks.

This code looks very nice, but i think that implementing a Lisp Interpreter in Python is some kind of cheating. Python is a high-level language, so you get very much for free. For an antipode, i suggest to have a look into Zozotez, a Lisp Interpeter in Brainfuck (which is a ridiculously low level toy language):
https://code.google.com/p/zozo...

Beautiful. Shouldn't cons be lambda x,y:[x]+[y]?

Thanks for another nice article. Would the "tokens.pop(0) # pop off ')'" be more clear as the faster, smaller byte-code, "del tokens[0]" since tokens[0], returned by pop(), isn't wanted.

Thanks for all the comments. Eric Cooper: I like your idea of eliminating the Procedure class. I had it because it is necessary to have access to the exp to do tail recursion elimination, but I don't need that in this version. bsagert: you are right that a proper repl needs to catch Exceptions. It also should be able to read multi-line input, which can't easily be done with the interface I have provided. Sainamdar: I did this because I still get a lot of interest in JScheme, and several people asked if I could do it in Python. Now the answer is: Yes I can! Massaro: you are right that a mutable pair can be implemented as a procedure with two variables. Or a vector of two elements. But the point is that if I did that, they would be different from Python's lists, and I couldn't use Python's map, etc.

Here is a more meta-circular implementation of procedures:

def procedure(parms, exp, env):
"A user-defined Scheme procedure."
return lambda *args: eval(exp, Env(parms, args, env))

Fabulous...!!

lisp is for faggots
join 4chan /prog/

in all honesty this is crap

Breathtaking

Concise and enlightening. Beautiful.

Great interpretation of that magical part of SICP, happy to see that this book still inspire people !

great

liked it

brilliant

awesome

great

really nice

good

superb

Really wonderful..

Very Usefull..

thats good one

How to test above examples in python 2.7.5

Thats remarkable...