[Python-bugs-list] [ python-Bugs-470429 ] relax data representation spec (original) (raw)

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Thu, 11 Oct 2001 16:31:39 -0700

Bugs item #470429, was opened at 2001-10-11 16:31 You can respond by visiting: http://sourceforge.net/tracker/?func=detail&atid=105470&aid=470429&group_id=5470

Category: None Group: Feature Request Status: Open Resolution: None Priority: 5 Submitted By: paul rubin (phr) Assigned to: Nobody/Anonymous (nobody) Summary: relax data representation spec

Initial Comment: I'm not sure how to submit this--"feature request" isn't really right. A documentation bug may also be involved. The specification for integers is in section 2.1.4 "Numeric Types" of the Python 2.1.1 library docs, which makes it unclear whether integers are supposed to be part of the language spec, or part of the library--so alternative implementations can implement integers differently and still conform to the language spec.

Anyway, the Numeric Types section says "Plain integers (also just called integers) are implemented using long in C, which gives them at least 32 bits of precision". I don't think a sentence like that should be in a specification, since it describes how something is implemented (using long in C) rather than how it should behave. For example, Jython uses java ints or longs rather than C longs, so the description that ints are implemented as C longs is simply incorrect. So if this section is supposed to be a specification, the reference to C longs should be removed, or clearly labelled as a description of how one particular implementation works.

More substantively, I think the requirement that ints have 32 bits of precision should be relaxed to 30 bits. That just means changing the specification-- implementations are free to continue supporting 32 bit ints. But it makes it easier to implement Python using 32-bit words with tag bits, a traditional implementation method for dynamically typed languages. Numerous processors even offer hardware support for tagged integers--not just special processors like Lisp machines, but also general purpose RISC cpu's like the Sparc. Since Python offers arbitrary sized longs and already doesn't promise a fixed size for ints, I don't think it would suffer by offering implementers a little more flexibility.

In a more philosophical vein, Python is a really cool language and the designers should begin to think of "success" in terms of more implementations being developed, native-code compilers being written, a possible ANSI standard some day, etc. So care should be taken to keep the formal specification as precise as possible, and free of requirements of things that are really just implementation hacks.

You can respond by visiting: http://sourceforge.net/tracker/?func=detail&atid=105470&aid=470429&group_id=5470