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<div class=Section1>
<p class=MsoNormal><span style='color:#1F497D'>#1 is definitely correct behavior,
consider:<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>IronPython 2.6 (2.6.10920.0) on
.NET 2.0.50727.4927<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>Type "help",
"copyright", "credits" or "license" for more
information.<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>>>> class c(object):<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>... def
__getitem__(self, index):<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>...
return index<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>...<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>>>> c()[0:1.2]<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>slice(0, 1.2, None)<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>It’s Python’s list
implementation which is converting indexes to integers so you’ll need to do
that as well. You can do that via IronPython.Runtime.Converter.ConvertToIndex
though.<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>On #2 in theory we don’t
let you override existing members w/ extension members. But __getitem__
is taking precedence here because we pick up the List<T> version later in
resolution via a .NET mapping than looking up members by name. But you
can define the integer overload for __getitem__ and forward it to the real
implementation. <o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>We could also consider just
adding slicing support for List<T> to IronPython natively </span><span
style='font-family:Wingdings;color:#1F497D'>J</span><span style='color:#1F497D'>
We probably can’t do that for all IList<T>’s though in case there’s
one that accepts negative or out of range indexes.<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<div style='border:none;border-left:solid blue 1.5pt;padding:0in 0in 0in 4.0pt'>
<div>
<div style='border:none;border-top:solid #B5C4DF 1.0pt;padding:3.0pt 0in 0in 0in'>
<p class=MsoNormal><b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>From:</span></b><span
style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>
users-bounces@lists.ironpython.com [mailto:users-bounces@lists.ironpython.com] <b>On
Behalf Of </b>Jeffrey Sax<br>
<b>Sent:</b> Wednesday, December 02, 2009 5:39 PM<br>
<b>To:</b> 'Discussion of IronPython'<br>
<b>Subject:</b> Re: [IronPython] Magic methods on CLR types<o:p></o:p></span></p>
</div>
</div>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal><span style='color:#1F497D'>I found 2 issues:<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>1. It looks like __index__ is
not called for slice arguments of non-Python objects (like
List<T>’s). Reading PEP 357 (which introduced __index__), I would
expect __index__ to always be called, so that I can be sure that the slice
components are either int, long, or NULL. (I haven’t verified this in CPython.)<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>2. If I supply a
__getitem__ method in my extension type (in my case with a strongly typed
ISlice parameter), the underlying CLR indexers are no longer picked up.<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>Extender assembly:<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>[assembly:
ExtensionType(typeof(List<>), typeof(ListExtensions<>))]<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>namespace Compatibility.Python {<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'> public static
class ListExtensions<T> {<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>
public static T __getitem__(List<T> a, ISlice slice) {<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>
return a[(int)slice.Start]; // Dummy<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>
}<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'> }<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>}<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>IP session 1:<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>IronPython 2.6 (2.6.10920.0) on
.NET 2.0.50727.4927<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>Type "help",
"copyright", "credits" or "license" for more
information.<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>>>> from
System.Collections.Generic import List<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>>>> a=List[int]()<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>>>> a.Add(55)<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>>>> a[0]<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>55<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>>>> a[0:1.2]<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>55<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>>>> b=[1,2,3,4]<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>>>> b[0:1.2]<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>Traceback (most recent call
last):<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'> File "<stdin>",
line 1, in <module><o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>TypeError: expected index value,
got float<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>>>> <o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>IP session 2:<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>IronPython 2.6 (2.6.10920.0) on
.NET 2.0.50727.4927<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>Type "help",
"copyright", "credits" or "license" for more
information.<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>>>> import clr<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>>>>
clr.AddReferenceToFile("Compatibility.Python")<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>>>> from
System.Collections.Generic import List<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>>>> a=List[int]()<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>>>> a.Add(55)<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>>>> a[0]<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>Traceback (most recent call
last):<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'> File
"<stdin>", line 1, in <module><o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>TypeError: expected ISlice, got
int<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>>>> <o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<div>
<div style='border:none;border-top:solid #B5C4DF 1.0pt;padding:3.0pt 0in 0in 0in'>
<p class=MsoNormal><b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>From:</span></b><span
style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>
users-bounces@lists.ironpython.com [mailto:users-bounces@lists.ironpython.com] <b>On
Behalf Of </b>Dino Viehland<br>
<b>Sent:</b> Tuesday, December 01, 2009 8:57 PM<br>
<b>To:</b> Discussion of IronPython<br>
<b>Subject:</b> Re: [IronPython] Magic methods on CLR types<o:p></o:p></span></p>
</div>
</div>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal><span style='color:#1F497D'>If you want IronPython to
recognize them you just need to create an assembly w/ ExtensionTypeAttribute
and have it point at the extended and extending types. Then the assembly
needs to be loaded into the ScriptRuntime using ScriptRuntime.LoadAssembly.<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>We still need to figure out our
story for recognizing and importing normal .NET extension methods that C#
supports.<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<div style='border:none;border-left:solid blue 1.5pt;padding:0in 0in 0in 4.0pt'>
<div>
<div style='border:none;border-top:solid #B5C4DF 1.0pt;padding:3.0pt 0in 0in 0in'>
<p class=MsoNormal><b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>From:</span></b><span
style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>
users-bounces@lists.ironpython.com [mailto:users-bounces@lists.ironpython.com] <b>On
Behalf Of </b>Jeffrey Sax<br>
<b>Sent:</b> Tuesday, December 01, 2009 5:27 PM<br>
<b>To:</b> 'Discussion of IronPython'<br>
<b>Subject:</b> [IronPython] Magic methods on CLR types<o:p></o:p></span></p>
</div>
</div>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>Is there a way to add magic methods like __repr__, __call__,
etc. to CLR types?<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoListParagraph style='text-indent:-.25in;mso-list:l0 level1 lfo2'><![if !supportLists]><span
style='mso-list:Ignore'>1.<span style='font:7.0pt "Times New Roman"'>
</span></span><![endif]>Can it be done in the external CLR assembly without
polluting the API for other languages? If so, how?<o:p></o:p></p>
<p class=MsoListParagraph style='text-indent:-.25in;mso-list:l0 level1 lfo2'><![if !supportLists]><span
style='mso-list:Ignore'>2.<span style='font:7.0pt "Times New Roman"'>
</span></span><![endif]>Can it be done using F# style type augmentations by
redefining such methods on the Python type corresponding to the CLR type? If
so, how?<o:p></o:p></p>
<p class=MsoListParagraph style='text-indent:-.25in;mso-list:l0 level1 lfo2'><![if !supportLists]><span
style='mso-list:Ignore'>3.<span style='font:7.0pt "Times New Roman"'>
</span></span><![endif]>If neither of these alternatives is possible, is there
a third way?<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>Thanks!<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>Jeffrey Sax<o:p></o:p></p>
</div>
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