human
Solve the following python programming problem given the following code:
def catalog_list(catalog, distro = None, print_versions = True, **kwargs) : 
    index = catalog.get_index () 
    def pretty_without_versions(result) : 
        return ('%s' % result ['bundle_name']) 
def pretty_with_versions(result) : 
        distros = index.distributions_for_bundle_by_version (result ['bundle_name']) 
        versions = index.versions_for_bundle (result ['bundle_name']) 
        version_strings = list () 
        for version in versions : 
            version_string = str (version) 
            if (distros.get (version) is not None) : 
                distro_string = ('(%s)' % ', '.join (sorted (distros.get (version)))) 
                version_string += ('=' + distro_string) 
                version_strings.append (version_string) 
final_version_string = ('[%s]' % ', '.join (version_strings)) 
        return ('%s %s' % (result ['bundle_name'], final_version_string)) 
pretty = (pretty_with_versions if print_versions else <MASK>) 
    def results() : 
        bundle_names = sorted (index.bundle_names ()) 
        for bundle_name in bundle_names : 
            d = dict () 
            if (distro and (distro not in index.distributions_for_bundle (bundle_name))) : 
                continue 
d ['bundle_name'] = bundle_name 
            d ['versions'] = index.versions_for_bundle (bundle_name) 
            d ['distros'] = index.distributions_for_bundle (bundle_name) 
            (yield DictResult (d, pretty = pretty)) 
return ResultSet (results) 
    
    Given the code above, what is a proper replacement for <MASK>?
assistant
#Here is a proper replacement for <MASK>.
def pretty_without_versions(