I like Raymond's suggestion (apparently adopted) that {1,2,3} is a frozenset literal. However, I also like the {{1,2,3}} syntax. So I would propose that {{}} become the literal for the *mutable* set, not the frozenset. So: frozenset() # empty frozenset {1,2,3} # frozenset literal {} # empty dict {1:2, 3:4} #dict literal {{}} (or set()) # empty mutable set {{1,2,3}} # set literal My rationale is as follows: 1. It visually distinguishes sets and frozensets, without making them take up a lot of space. If people see the {{}}, they will be reminded that this set is mutable. 2. In Raymond's example, his point was that most people don't want a mutable literal - they would be better served by a frozenset. However, sometimes you *do* want to add elements to a set literal. For example: # I am parsing the configuration file for a pure-python webserver. # The config file allows me to add new filetype extensions # that will be served. # Default HTML extensions: HTML_EXTS = {{'.html', '.htm'}} # later, when going through config file: if filetype.handler == HTMLHandler: HTML_EXTS.add(filetype.ext) I know that this can be done other ways (set(['.html', '.htm'])), but I like the way this looks. Thanks, Van P.S.: The bikeshed should be yellow.