[IronPython] clr.ImportExtensions are not available outside module ?

daniel kottow dkottowk at yahoo.com
Fri May 13 14:41:25 CEST 2011


Hello Dino,
I don't think I want to delve into more complexity, thank you :-)

What I was trying to say that, unfortunately, I do not see a way to encapsulate 
my extension methods written in C# so that a person doing only python does not 
have to worry about it -
on the other hand, i reckon it is also not such a big deal to write some 
clr.ImportExtensions on the beginning of a module and then the developer *can* 
forget on how the methods got there.

Btw, in order to use the methods interactively, I now start my session with "-i 
ironstuff" and everything is fine, i get my classes with their extension methods 
on the cmd line... very nice.

Thank you for time.
Daniel.





----- Original Message ----
From: Dino Viehland <dinov at microsoft.com>
To: Discussion of IronPython <users at lists.ironpython.com>
Sent: Thu, May 12, 2011 3:50:01 PM
Subject: Re: [IronPython] clr.ImportExtensions are not available outside module 
?

Daniel wrote:
> Ok.
> I am not sure what you mean by similar to import clr, though.

It's similar to import clr in that importing clr not only gives you the clr 
module
but also makes .NET members available to the module which imported clr.
For example before doing "import clr" calling .ToString() on an object will
raise an AttributeError but afterwards it will call the .NET ToString method.

If you'd like to provide a set of globally available extension methods 
specifically
for IronPython users you could use ExtensionTypeAttribute (which is defined
in the DLR outer layer).  IronPython will look for that attribute declared on an
assembly.  The attribute will give a type to extend and a type to pull the 
extension
methods from.  All you need to do is load the assembly into the script runtime
either via the hosting APIs or clr.AddReference.  This was the mechanism we 
originally used to add the Python methods to the .NET types like string (we now
hard code the types for Python rather reflecting over the types at startup, but
the mechanism remains for backwards compat).  

> 
> Because in my example, clr is available from outside test; its just named
> test.clr...
> Let me give you another example which is closer on how I ran into this...
> 
> Lets say you have in C#:
> 
> --- iron.Example.cs
> 
> namespace iron
> {
>     public class Example
>     {
>         public Example()
>         {
>         }
> 
>         public int foo()
>         {
>             return 1;
>         }
>     }
> 
>     public static class ExampleExtension
>     {
>         public static int bar(this Example example)
>         {
>             return example.foo() + 1;
>         }
> 
>     }
> }
> 
> --- EOF
> 
> Then I define an example.py to wrap this up:
> 
> --- test.py
> 
> import clr
> clr.AddReference("iron")
> import iron
> clr.ImportExtensions(iron.ExampleExtension)
> 
> # lets use this just to test it out
> 
> e = iron.Example()
> print e.foo()
> print e.bar()
> 
> --- EOF
> 
> now on my command line I get
> 
> >>> import example
> 1
> 2
> >>> ex = example.iron.Example()
> >>> ex.foo()
> 1
> >>> ex.bar()
> Traceback (most recent call last):
>   File "<stdin>", line 1, in <module>
> AttributeError: 'Example' object has no attribute 'bar'
> 
> And so I don't find a nice way to wrap my C# functionality in just one python
> module,
> 
> where I whish I could offer the extension methods just like any other
> method...
> or is my import strategy somehow flawed ?
> 
> Greetings,
> Daniel
> 
> 
> 
> 
> 
> namespace native
> {
>     public class Example
>     {
>     }
> 
>     public static class ExampleExtension
>     {
>          public static void
>     }
> 
> add some extension methods to it, and then want to import everything in
> one
> python stub module. E.g.
> 
> 
> 
> 
> 
> ----- Original Message ----
> From: Dino Viehland <dinov at microsoft.com>
> To: Discussion of IronPython <users at lists.ironpython.com>
> Sent: Thu, May 12, 2011 1:01:33 PM
> Subject: Re: [IronPython] clr.ImportExtensions are not available outside
> module
> ?
> 
> 
> 
> Daniel wrote:
> > Just as Dave Wald, I have also trying out the ImportExtensions methods
> > which I personally find very useful, thank you for implementing. Everything
> is
> > working fine on using 2.7 (and .net 4), but extension methods loaded by
> one
> > module seem not available on another...
> 
> This is by design.  It works similar to how "import clr" only effects the
> current module
> and how extension methods work in C# where they are scoped by file.  So if
> you
> want extension methods available in a file you'll need to import them in that
> file.
> 
> If they were globally scoped it would be easy for one module to break
> another by
> bringing in the 'wrong' extension methods.
> 
> >
> >
> > I will stick to Dave's code exmaple:
> >
> > import clr
> > clr.AddReference("System.Core")
> > import System
> > from System import Linq
> >
> > clr.ImportExtensions(Linq)
> >
> > class Product(object):
> >      def __init__(self, cat, id, qtyOnHand ):
> >          self.Cat = cat
> >          self.ID = id
> >          self.QtyOnHand = qtyOnHand
> >          self.Q = self.QtyOnHand
> >
> > If I put this into a file, lets say test.py and now use the module on the
> > command line:
> >
> > >>> import test
> > >>> products = [test.Product('food', i, 10) for i in range(3)]
> > >>>
> > >>>
> > >>> products.Where
> > Traceback (most recent call last):
> >   File "<stdin>", line 1, in <module>
> > AttributeError: 'list' object has no attribute 'Where'
> >
> > The linq extensions are not available. I have to re-import them:
> >
> > >>> test.clr.ImportExtensions(test.Linq)
> > >>> products.Where
> > <built-in method Where of list object at 0x000000000000002B>
> > >>>
> >
> > Is this a current limitation, or should I be doing things differently ?
> > Any help appreciated.
> >
> > Greetings,
> > Daniel
> > _______________________________________________
> > Users mailing list
> > Users at lists.ironpython.com
> > http://lists.ironpython.com/listinfo.cgi/users-ironpython.com
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