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Python and the Programmer
A Conversation with Bruce Eckel, Part I
by Bill Venners
Jun 2, 2003

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Number 9: Not Backwards Compatible in Exchange for Pain

Bill Venners: In your keynote, your ninth reason for loving Python was, "Not backwards compatible in exchange for pain." Could you speak a bit about that?

Bruce Eckel: That's primarily directed at C++. To some degree you could say it refers to Java because Java was derived primarily from C++. But C++ in particular was backwards compatible with C, and that justified lots of language issues. On one hand, that backwards compatibility was a great benefit, because C programmers could easily migrate to C++. It was a comfortable place for C programmers to go. But on the other hand, all the features that were compromised for backwards compatibility was the great drawback of C++.

Python isn't backwards compatible with anything, except itself. But even so, the Python designers have actually modified some fundamental things in order to fix the language in places they decided were broken. I've always heard from Sun that backwards compatibility is job one. And so even though stuff is broken in Java, they're not going to fix it, because they don't want to risk breaking code. Not breaking code always sounds good, but it also means we're going to be in pain as programmers.

One fundamental change they made in Python, for example, was "type class unification." In earlier versions, some of Python's primitive types were not first class objects with first class characteristics. Numbers, for example, were special cases like they are in Java. But that's been modified so now I can inherit from integer if I want to. Or I can inherit from the modified dictionary class. That couldn't be done before. After a while it began to be clear that it was a mistake, so they fixed it.

Now in C++ or Java, they'd say, "Oh well, too bad." But in Python, they looked at two issues. One, they were not breaking anybody's existing world, because anyone could simply choose to not upgrade. I think that could be an attitude taken by Java as well. And two, it seemed relatively easy to fix the broken code, and the improvement seemed worth the code-fixing work. I find that attitude so refreshing, compared to the languages I'd used before where they said, "Oh, it's broken. We made a mistake, but you'll have to live with it. You'll have to live with our mistakes."

Next Week

Come back Monday, June 9 for Part I of a conversation with Java's creator James Gosling. I am now staggering the publication of several interviews at once, to give the reader variety. The next installment of this interview with Bruce Eckel will appear on Monday, June 23. If you'd like to receive a brief weekly email announcing new articles at, please subscribe to the Artima Newsletter.

Talk Back!

Have an opinion about programmer productivity, backwards compatibility, or breaking code versus programmer pain. Discuss this article in the News & Ideas Forum topic, Python and the Programmer.


Bruce Eckel's Mindview, Inc.:

Bruce Eckel's essay on checked exceptions: Does Java Need Checked Exceptions?:

Bruce Eckel's Public and In-House Seminars:

Bruce Eckel's Weblog:, the Python Language Website:

Introductory Material on Python:

Python Tutorial:

Python FAQ Wizard:

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