def get_available_palettes(chosen_palette):
result = None<EOL>try:<EOL><INDENT>result = ALL_PALETTES[:ALL_PALETTES.index(chosen_palette)+<NUM_LIT:1>]<EOL><DEDENT>except ValueError:<EOL><INDENT>pass<EOL><DEDENT>return result<EOL>
Given a chosen palette, returns tuple of those available,
        or None when not found.

        Because palette support of a particular level is almost always a
        superset of lower levels, this should return all available palettes.

        Returns:
            Boolean, None: is tty or None if not found.