[Python-Dev] PEP 460: allowing %d and %f and mojibake (original) (raw)

Guido van Rossum guido at python.org
Tue Jan 14 16:59:44 CET 2014

On Tue, Jan 14, 2014 at 12:20 AM, Greg Ewing <greg.ewing at canterbury.ac.nz> wrote:

Guido van Rossum wrote:

I've now looked at asciistr. (Thanks Glenn and Ethan for the link.) Now that I (hopefully) understand it, I'm worried that a text processing algorithm that uses asciistr might under hard-to-predict circumstances (such as when the arguments contain nothing of interest to the algorithm) might return an asciistr instance instead of a str or bytes instance, It seems to me that any algorithm with that property has a genuine ambiguity as to what it should return in that case. Arguably, returning an asciistr would be the right thing to do, because that would allow it to be used as a component of a larger algorithm that was polymorphic with respect to text/bytes.

Here's an example of what I mean:

def spam(a): r = asciistr('(') if a: r += a.strip() r += asciistr(')') return r

The argument must be a string.

If I call spam(''), a's type is never concatenated with r, so the return value is an asciistr. To fix this particular case, we could drop the "if a:" part. But it could be more significant, e.g. it could be something like "if a contains any digits". The general fix would be to add

else: r += a[:0]

but that's still an example of the awkwardness that asciistr() is trying to avoid.

-- --Guido van Rossum (python.org/~guido)

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