On Feb 10, 9:52 pm, "Gabriel Genellina" <gagsl-...@yahoo.com.ar> wrote: > En Wed, 11 Feb 2009 00:31:26 -0200, <mark.sea...@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. > Seehttp://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
Thanks very much, Gabriel. This is very good start for me. This works for predefined class. How about a situation where the fields are added dynamically (as from reading in from an xml file). For example, if I were to now add another element: >>> point.z = 30 >>> print list(point) [10, 20] >>> dir(point) ['__class__', '__ctypes_from_outparam__', '__delattr__', '__ dict__', '__doc__', '__getattribute__', '__getitem__', '__ha sh__', '__init__', '__module__', '__new__', '__reduce__', '_ _reduce_ex__', '__repr__', '__setattr__', '__str__', '__weak ref__', '_b_base_', '_b_needsfree_', '_fields_', '_objects', 'x', 'y', 'z'] I don't know why the iterator (where ever it is) didn't get incremented. Thanks for any insight. Mark -- http://mail.python.org/mailman/listinfo/python-list
