On Wed, Feb 10, 2016 at 11:20:38PM +0100, Georg Brandl wrote: > This came up in python-ideas, and has met mostly positive comments, > although the exact syntax rules are up for discussion.
Nicely done. But I would change the restrictions to a simpler version. Instead of five rules to learn: > The current proposal is to allow underscores anywhere in numeric literals, > with > these exceptions: > > * Leading underscores cannot be allowed, since they already introduce > identifiers. > * Trailing underscores are not allowed, because they look confusing and don't > contribute much to readability. > * The number base prefixes ``0x``, ``0o``, and ``0b`` cannot be split up, > because they are fixed strings and not logically part of the number. > * No underscore allowed after a sign in an exponent (``1e-_5``), because > underscores can also not be used after the signs in front of the number > (``-1e5``). > * No underscore allowed after a decimal point, because this leads to ambiguity > with attribute access (the lexer cannot know that there is no number literal > in ``foo._5``). change to a single rule "one or more underscores may appear between two (hex)digits, but otherwise nowhere else". That's much simpler to understand than a series of restrictions as given above. That would be your second restrictive rule: "Multiple consecutive underscore allowed, but only between digits." That forbids leading and trailing underscores, underscores inside or immediately after the leading number base (since x, o and b aren't digits), and immediately before or after the sign, decimal point or e|E exponent symbol. > There appears to be no reason to restrict the use of underscores otherwise. I don't like underscores immediately before the . or e|E in floats either: 123_.000_456 The dot is already visually distinctive enough, as is the e|E, and placing an underscore immediately before them doesn't aid in grouping the digits. > Instead of the liberal rule specified above, the use of underscores could be > limited. Common rules are (see the "other languages" section): > > * Only one consecutive underscore allowed, and only between digits. > * Multiple consecutive underscore allowed, but only between digits. I don't think there is any need to restrict it to only a single underscore. There are uses for more than one: Fraction(3__141_592_654, 1_000_000_000) hints that the 3 is somewhat special (for obvious reasons). -- Steve _______________________________________________ Python-Dev mailing list [email protected] https://mail.python.org/mailman/listinfo/python-dev Unsubscribe: https://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com