Why MIT now uses python instead of scheme for its undergraduate CSĀ program

By Chas Emerick

This week, I find myself lucky enough to be at the International Lisp Conferenceat MIT in Cambridge, MA.  I won’t get into why I’m here right now, for those of you who might be surprised.  The purpose of this post is simply to paraphrase what Gerald Jay Sussman, one of the original creators of Scheme, said yesterday in an a brief impromptu talk about why the computer science department at MIT had recently switched to using python in its undergraduate program.  This change is something that was widely panned when it was announced by many people all across the programming and computing world from various disciplines, so it seems worthwhile to try to document what Prof. Sussman said.

(The impromptu talk happened much after Monday’s formal talks and presentations, and I don’t think that anyone was recording Prof. Sussman’s remarks.  If anyone does have a recording, by all means, post it, and I’ll link to it here — and probably just drop my paraphrasing.)

This is all from memory, so I’ll just apologize ahead of time for any errors or misinterpretations I propagate. If anyone has any corrections, by all means, leave a comment (try to keep your debate reflex in check, though).  In a couple of places, I’ve added notes in italics.  Just to keep things simple and concise, the following is written in first-person perspective:

When we conceived of scheme in the 1970’s, programming was a very different exercise than it is now.  Then, what generaly happened was a programmer would think for a really long time, and then write just a little bit of code, and in practical terms, programming involved assembling many very small pieces into a larger whole that had aggregate (did he say ‘emergent’?) behaviour.  It was a much simpler time.

Critically, this is the world for which scheme was originally designed.  Building larger programs out of a group of very small, understandable pieces is what things like recursion and functional programming are built for.

The world isn’t like that anymore.  At some point along the way (he may have referred to the 1990’s specifically), the systems that were being built and the libraries and components that one had available to build systems were so large, that it was impossible for any one programmer to be aware of all of the individual pieces, never mind understand them.  For example, the engineer that designs a chip, which now have hundreds of pins generally doesn’t talk to the fellow who’s building a mobile phone user interface.

The fundamental difference is that programming today is all about doing science on the parts you have to work with.  That means looking at reams and reams of man pages and determining that POSIX does this thing, but Windows does this other thing, and patching together the disparate parts to make a usable whole.

Beyond that, the world is messier in general.  There’s massive amounts of data floating around, and the kinds of problems that we’re trying to solve are much sloppier, and the solutions a lot less discrete than they used to be.

Robotics is a primary example of the combination of these two factors.  Robots are magnificently complicated and messy, with physical parts in the physical world.  It doesn’t just move forward along the ground linearly and without interruption: the wheels will slip on the ground, the thing will get knocked over, etc.

This is a very different world, and we decided that we should adjust our curriculum to account for that.  So, a committee (here, Prof. Sussman peaked his hands over his head, which I interpreted to indicated pointy-headedness) got together and decided that python was the most appropriate choice for future undergraduate education.  Why did they choose python?  Who knows, it’s probably because python has a good standard library for interacting with the robot.

That is my best paraphrasing of Prof. Sussman’s remarks.  I spoke with him briefly earlier today, primarily to ask his permission for me to post this sort of first-person paraphrasing; he replied: “Sure, as long as you paraphrase me accurately.”  Hopefully I succeeded; I’ll mention again my solicitation for corrections in the comments.

As a short addendum, while I had Prof. Sussman’s ear, I asked him whether he thought that the shift in the nature of a typical programmer’s world minimizes the relevancy of the themes and principles embodied in scheme.  His response was an emphatic ‘no’; in the general case, those core ideas and principles that scheme and SICP have helped to spread for so many years are just as important as they ever were.  However, he did say that starting off with python makes an undergraduate’s initial experiences maximally productive in the current environment.  To that, I suggested that that dynamic makes it far easier to “hook” undergrads on “computer science” and programming, and retaining people’s interest and attracting people to the field(s) is a good thing in general; Prof. Sussman agreed with that tangential point.