load all icons found in path, subdirs 'icons/appname

def _load(self):
        """load all icons found in path, subdirs 'icons/appname'"""
        # loop over system path
        if self._loaded:
            return
        icon_paths = ['/usr/local/share/meqtrees'] + sys.path
        for path in icon_paths:
            path = path or '.'
            # for each entry, try <entry>/icons/<appname>'
            for a, b in [('icons', self._appname), (self._appname, 'icons')]:
                trydir = os.path.join(path, a, b)
                _dprint(3, 'trying icon path', trydir)
                try:
                    files = os.listdir(trydir)
                except:
                    continue
                _dprint(3, len(files), 'entries in', trydir)
                # loop over all files
                nicons = 0
                for f in files:
                    (name, ext) = os.path.splitext(f);  # check extension
                    if ext in ('.png', '.xpm', '.gif'):
                        f = os.path.join(trydir, f)
                        try:
                            pm = QPixmap(f)
                        except:
                            _dprint(3, 'error loading icon', name, sys.exc_value())
                            continue
                        # register pixmap
                        self._pixmaps[name] = QPixmapWrapper(pm)
                        nicons += 1
                        _dprint(4, 'loaded icon', f)
                    else:
                        _dprint(4, 'ignoring entry', f)
                _dprint(1, nicons, 'icons loaded from ', trydir)
                self._loaded = True