[Python-Dev] PEP 260: simplify xrange()

Guido van Rossum guido@digicool.com
Tue, 26 Jun 2001 13:59:55 -0400

Here's another sweet and short PEP.  What do folks think?  Is
xrange()'s complexity really worth having?

--Guido van Rossum (home page: http://www.python.org/~guido/)

PEP: 260
Title: Simplify xrange()
Version: $Revision: 1.1 $
Author: guido@python.org (Guido van Rossum)
Status: Draft
Type: Standards Track
Python-Version: 2.2
Created: 26-Jun-2001
Post-History: 26-Jun-2001


    This PEP proposes to strip the xrange() object from some rarely
    used behavior like x[i:j] and x*n.


    The xrange() function has one idiomatic use:

        for i in xrange(...): ...

    However, the xrange() object has a bunch of rarely used behaviors
    that attempt to make it more sequence-like.  These are so rarely
    used that historically they have has serious bugs (e.g. off-by-one
    errors) that went undetected for several releases.

    I claim that it's better to drop these unused features.  This will
    simplify the implementation, testing, and documentation, and
    reduce maintenance and code size.

Proposed Solution

    I propose to strip the xrange() object to the bare minimum.  The
    only retained sequence behaviors are x[i], len(x), and repr(x).
    In particular, these behaviors will be dropped:

        x[i:j] (slicing)
        x*n, n*x (sequence-repeat)
        cmp(x1, x2) (comparisons)
	i in x (containment test)
        x.tolist() method
        x.start, x.stop, x.step attributes

    By implementing a custom iterator type, we could speed up the
    common use, but this is optional (the default sequence iterator
    does just fine).

    I expect it will take at most an hour to rip it all out; another
    hour to reduce the test suite and documentation.


    This PEP only affects the xrange() built-in function.


    Somebody's code could be relying on the extended code, and this
    code would break.  However, given that historically bugs in the
    extended code have gone undetected for so long, it's unlikely that
    much code is affected.


    This document has been placed in the public domain.

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