[IronPython] What C# methods do repr and str use?

Thu May 29 00:05:14 CEST 2008

On Wed, May 28, 2008 5:19 pm, Dino Viehland said:
> We could definitely add a __repr__ for the normal .NET lists (and even
> other standard types like Dictionary).  Maybe something like Python's
> set's repr so it'd look like:
>
> List[object]([2, 3, 4])
>
> Does that look good?

For our particular usage (new students using IronPython as their first
language) this doesn't look so good. But if there will be a way that we
can write C# code which can be loaded by Ruby, Python, etc and we can
override the repr, then we can adapt.

Currently, we're just using Python's list rather than the normal .NET
generic list type. That works great (for Python). Will there be a list
that will look native across dynamic languages?

-Doug

> -----Original Message-----
> From: users-bounces at lists.ironpython.com
> [mailto:users-bounces at lists.ironpython.com] On Behalf Of Douglas S. Blank
> Sent: Wednesday, May 28, 2008 2:08 PM
> To: Discussion of IronPython
> Subject: Re: [IronPython] What C# methods do __repr__ and __str__ use?
>
> Dino Viehland wrote:
>> The problem w/ a common __repr__ is that each language will
>> presumably have different syntax for creating the object.  For
>> example a better repr in Python might be:
>>
>> Pixel(255,255,128)
>>
>> Where Ruby should probably display something like:
>>
>> Pixel.new(255,255,128)
>
> Agreed. But maybe there can be some name *patterns* that if implemented
> once would suffice for most languages. I'm not too worried about this
> though.
>
>> Having a repr of [255,255,128] isn't that meaningful because if I
>> copy and paste that into my code I get a list instead of a Pixel
>> back.
>
> Sorry, I switched issues on you :) That was the point of that example...
> generic lists don't look like lists at all. I'm actually more concerned
> with this example than the previous. A generic list of ints, strings,
> etc. ought to be able to have a better representation in IP.
>
>> We could revisit what our default repr does for .NET objects
>> that override ToString.  We discussed it once on the list long ago
>> but that was mainly focused on dealing w/ multi-line ToStrings if I
>> recall correctly - the thought of playing better with multiple
>> languages wasn't much of an issue back then for us.
>>
>> So basically I am open to suggestions :)
>
> Perhaps generic lists could inherit a version of Python List's __repr__?
> (But of course, not just for Python, but for Ruby, etc.)
>
> Thanks!
>
> -Doug
>
>> -----Original Message----- From: users-bounces at lists.ironpython.com
>> [mailto:users-bounces at lists.ironpython.com] On Behalf Of Douglas S.
>> Blank Sent: Wednesday, May 28, 2008 1:47 PM To: Discussion of
>> IronPython Subject: Re: [IronPython] What C# methods do __repr__ and
>> __str__ use?
>>
>> Dino Viehland wrote:
>>> You'll want to implement the ICodeFormattable interface.  It looks
>>> like we don't pick up a method that's just named __repr__ right
>>> now. I could see us fixing that but I wouldn't think it's a high
>>> priority unless someone finds implementing ICodeFormattable
>>> burdensome.
>>
>> Thanks, that did the trick (sample attached below)! It isn't
>> burdensome, but I wonder about what will happen when we use IronRuby,
>> too? We'll we need repr methods for each language?
>>
>> I also wonder if things like a generic list couldn't pick up a
>> reasonable default __repr__ for use in all DLR languages.
>>
>> We're using the .NET languages in an educational environment for new
>> students. Currently, we're going to have to add the __repr__ to all
>> classes, and add subclasses to all types for which there isn't a
>> reasonable repr default. For example, there is a pretty big
>> difference between: "[255, 255, 128]" and "<List<GraphicsCore+Pixel>
>> object at 0x000002C [List<GraphicsCore+Pixel>]>" or whatever it might
>> be.
>>
>> In any event, we have a work around now; thanks again!
>>
>> -Doug
>>
>> using System; using IronPython.Runtime; // for ICodeFormattable using
>> Microsoft.Scripting.Runtime; // for CodeContext public class TestMe :
>> ICodeFormattable { public virtual string __repr__(CodeContext
>> context) { return String.Format("<Hi Mom>"); } }
>>
>>
>>> -----Original Message----- From: users-bounces at lists.ironpython.com
>>>  [mailto:users-bounces at lists.ironpython.com] On Behalf Of Douglas
>>> S. Blank Sent: Wednesday, May 28, 2008 12:22 PM To: Discussion of
>>> IronPython Subject: Re: [IronPython] What C# methods do __repr__
>>> and __str__ use?
>>>
>>> Anyone have an answer for this: I can't write C# code that has its
>>> own method for use in repr(). Am I missing something?
>>>
>>> -Doug
>>>
>>> Douglas S. Blank wrote:
>>>> On Fri, May 23, 2008 3:37 pm, Toni Alatalo said:
>>>>> Douglas S. Blank kirjoitti:
>>>>>> will use it? Likewise, what C# method is used in Python's
>>>>>> str(obj)?
>>>>>>
>>>>> i don't know, but would guess ToString() .. and wonder about it
>>>>>  if it wasn't that but something else :o repr() can't guess, i
>>>>> don't think there's an equivalent in .net, but can very well be
>>>>>  mistaken there.
>>>> It looks like the C# method __str__ is used for the Python
>>>> method, but in IP2B2 the C# method __repr__ is getting
>>>> overwritten by an auto generated method. Is that a bug, or is
>>>> there something I'm missing?
>>>>
>>>> $ ipy2 -i python/graphics.py
>>>>>>> pm = Pixmap() pm.getPixel(0,0)                    # What is
>>>>>>>  this calling?
>>>> <Pixel object at 0x2B>
>>>>>>> pm.getPixel(0,0).__repr__()         # This is repr() too
>>>> '<GraphicsCore+Pixel object at 0x2C [GraphicsCore+Pixel]>'
>>>>>>> pm.getPixel(0,0).__Repr__()         # This is mine
>>>> '<Pixel at (0,0)>'
>>>>>>> pm.getPixel(0,0).__str__()          # That is mine, and
>>>>>>> str()
>>>>>>>
>>>> '<Pixel at (0,0)>'
>>>>>>> pm.getPixel(0,0).ToString()         # Used by __repr__
>>>> 'GraphicsCore+Pixel'
>>>>
>>>> -Doug
>>>>
>>>>>> -Doug
>>>>>>
>>>>> ~Toni
>>>>>
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-- 
Douglas S. Blank
Associate Professor, Bryn Mawr College
http://cs.brynmawr.edu/~dblank/
Office: 610 526 6501