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

[guido.van.rossum]

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