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python-peps / pep-0260.txt

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

Abstract

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


Problem

    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

    I also propose to change the signature of the PyRange_New() C API
    to remove the 4th argument (the repetition count).

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


Scope

    This PEP affects the xrange() built-in function and the
    PyRange_New() C API.


Risks

    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.


Transition

    For backwards compatibility, the existing functionality will still
    be present in Python 2.2, but will trigger a warning.  A year
    after Python 2.2 final is released (probably in 2.4) the
    functionality will be ripped out.


Copyright

    This document has been placed in the public domain.


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