def on_attribute(self, node):    # ('value', 'attr', 'ctx')
        ctx = node.ctx.__class__
        if ctx == ast.Del:
            return delattr(sym, node.attr)

        sym = self.run(node.value)
        if node.attr not in UNSAFE_ATTRS:
            try:
                return getattr(sym, node.attr)
            except AttributeError:
                pass

        obj = self.run(node.value)
        fmt = "%s does not have member '%s'"
        if not isgroup(obj):
            obj = obj.__class__
            fmt = "%s does not have attribute '%s'"
        msg = fmt % (obj, node.attr)
        self.raise_exception(node, exc=AttributeError, msg=msg)
extract attribute
dataset/ETHPy150Open xraypy/xraylarch/lib/interpreter.py/Interpreter.on_attribute