'Return the module (a CIX <scope ilk="blob">) and package (a
CIX <scope ilk="class"> element) for the given package name. If
the package definition cannot be found, this returns
(None, None).'

def mod_and_pkg_from_pkg_name(self, pkg_name):

    if (pkg_name in self._mod_from_pkg_name):
        mod = self._mod_from_pkg_name[pkg_name]
        if (mod is not None):
            return (mod, mod.names.get(pkg_name))
    for (mod, pkg_names) in self._generator:
        if (mod is None):
            continue
        if (pkg_name in pkg_names):
            return (mod, mod.names.get(pkg_name))
    return (None, None)
