def METHOD_NAME(self):
    addon = self.cleaned_data['addon']
    try:
        zip_file = zipfile.ZipFile(addon)
    except:
        raise forms.ValidationError(_("Could not unzip file."))
    bad_file = zip_file.testzip()
    zip_file.close()
    del zip_file
    if bad_file:
        raise forms.ValidationError(_('Bad file/s found in ZIP archive.'))
    return addon