On 01/02/2014 06:24 PM, Guido van Rossum wrote:
The current behavior is intentional, and the ambiguity of strings themselves being iterables is the main reason. Since startswith() is almost always called with a literal or tuple of literals anyway, I see little need to extend the semantics. (I notice that you don't actually give any examples where the iterator would be useful -- have you encountered any, or are you just arguing for consistency's sake?)
This is driven by a real-world example wherein a large number of prefixes stored in a set, necessitating: any('spam'.startswith(c) for c in prefixes) # or 'spam'.startswith(tuple(prefixes)) However, .startswith doesn't seem to be the only example of this, and the other examples are free of the string/iterable ambiguity: isinstance(x, {int, float}) I do agree that it's definitely important to retain the behaviour of: 'spam'.startswith('sz') At same time, I think the non-string iterable problem is already fairly well-known and not a source of great confusion. How often has one typed: isinstance(x, Iterable) and not isinstance(x, str) Cheers, James Powell follow: @dontusethiscode + @nycpython attend: nycpython.org + flask-nyc.org read: seriously.dontusethiscode.com