Iterable Ctypes Struct

[Gabriel Genellina]

En Wed, 11 Feb 2009 00:31:26 -0200, <mark.seagoe at gmail.com> escribió:

> I like the ability to access elements of a struct such as with ctypes
> Structure:
>>>> myStruct.elementName1
> 4
>
> What I like about it is there are no quotes needed.
>
> What I don't like about it is that it's not iterable:
>>>> for n in myStruct:  <== gives error
>>>>    print n
>
> I don't want to force the end user to have preknowledge of the element
> names.

Note that those names are available as the _fields_ class attribute

> Has anyone subclassed ctypes Structure based class to be iterable?
> Before a noob starts trying to do this, is it possible?  How to
> approach it?

The easiest way would be to define __getitem__ accepting index 0, 1, 2...  
until the last defined field.
See http://docs.python.org/reference/datamodel.html#object.__getitem__

<code>
 from ctypes import Structure

class IterableStructure(Structure):
   def __getitem__(self, i):
     if not isinstance(i, int):
       raise TypeError('subindices must be integers: %r' % i)
     return getattr(self, self._fields_[i][0])

</code>

This was tested as much as you see here:

py> from ctypes import c_int
py>
py> class POINT(IterableStructure):
...     _fields_ = [("x", c_int),
...                 ("y", c_int)]
...
py> point = POINT(10, 20)
py> print point.x, point.y
10 20
py> for field in point:
...   print field
...
10
20
py> print list(point)
[10, 20]

-- 
Gabriel Genellina