[Python-checkins] r42549 - peps/trunk/pep-0357.txt

Wed Feb 22 05:00:20 CET 2006

Author: guido.van.rossum
Date: Wed Feb 22 05:00:18 2006
New Revision: 42549
Modified:
 peps/trunk/pep-0357.txt
Log:
Travis's changes.
Modified: peps/trunk/pep-0357.txt
==============================================================================

--- peps/trunk/pep-0357.txt	(original)
+++ peps/trunk/pep-0357.txt	Wed Feb 22 05:00:18 2006
@@ -12,7 +12,7 @@
 
 This PEP proposes adding an nb_index slot in PyNumberMethods and an
 __index__ special method so that arbitrary objects can be used
- whenever only integers are called for in Python, such as in slice
+ whenever integers are explicitly needed in Python, such as in slice
 syntax (from which the slot gets its name).
 
 Rationale
@@ -62,15 +62,13 @@
 def __index__(self):
 return obj
 
- Where obj must be either an int or a long or another object that has the
- __index__ special method (but not self).
+ where obj must be either an int or a long. 
 
 3) A new C-API function PyNumber_Index will be added with signature
 
 Py_ssize_t PyNumber_Index (PyObject *obj)
 
- which will special-case integer and long integer objects but otherwise
- return obj->ob_type->tp_as_number->nb_index(obj) if it is available. 
+ which will return obj->ob_type->tp_as_number->nb_index(obj) if it is available. 
 A -1 will be returned and an exception set on an error. 
 
 4) A new operator.index(obj) function will be added that calls
@@ -100,7 +98,7 @@
 7) Add the operator.index(x) function.
 
 
-Possible Concerns
+Discussion Questions
 
 Speed: 
 
@@ -109,7 +107,7 @@
 instructions. The only change will be that what used to generate
 an error will now be acceptable.
 
- Why not use nb_int which is already there?:
+ Why not use nb_int which is already there?
 
 The nb_int method is used for coercion and so means something
 fundamentally different than what is requested here. This PEP
@@ -119,7 +117,7 @@
 thing is that float objects already define the nb_int method, but
 float objects *should not* be used as indexes in a sequence.
 
- Why the name __index__?:
+ Why the name __index__?
 
 Some questions were raised regarding the name __index__ when other
 interpretations of the slot are possible. For example, the slot
@@ -139,10 +137,15 @@
 makes sense to return the C-integer directly and not wrapped
 in a Python int object. 
 
+ Why can't __index__ return any object with the nb_index method?
+
+ This would allow infinite recursion in many different ways that are not
+ easy to check for. This restriction is similar to the requirement that 
+ __nonzero__ return an int or a bool. 
+
 Reference Implementation
 
- Submitted as patch 1429591 to SourceForge. This patch number does
- not contain implementation 5.
+ Submitted as patch 1436368 to SourceForge. 
 
 Copyright
 
