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PEP 260 -- Simplify xrange()

Title:Simplify xrange()
Author:guido at (Guido van Rossum)
Type:Standards Track


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

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).


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


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.


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.