[IPython-dev] Next-gen result printing using generics

Walter Dörwald walter at livinglogic.de
Sat May 26 08:34:59 EDT 2007

Ville M. Vainio wrote:
> On 5/26/07, Walter Dörwald <walter at livinglogic.de> wrote:
>> That was going through my head too. However the current display hook
>> fires for subclasses of Table too (that's why you can type ils instead
>> of ils()). For this to work, we'd need a when_subclass() decorator in
>> simplegeneric.
> Doesn't when_type do this?

No, it checks the class of the argument not the argument itself:

In [1]: from simplegeneric import *
In [2]: @generic
    ...: def foo(x):
    ...:     print x
In [3]: @foo.when_type(int)
    ...: def foo_int(x):
    ...:     print "int", x
In [4]: foo(42)
int 42
In [5]: foo(int)
<type 'int'>

> I see the MRO mentioned in the sources anyway...

Yes, but it iterates the MRO of the class of the argument to find an 
implementation, so passing the class will iterate the MRO of type (or 
types.ClassType for old-style classes).


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