[Python-Dev] Format strings, Unicode, and Py2.7: need clarification (original) (raw)

Hobson Lane hobsonlane at gmail.com
Thu May 18 20:20:58 EDT 2017

Yea, must probably should have been should (unless indicated by the method name). I forgot about the many methods that don't. But the names of these methods, like split(), imply the types that they return.

Your example reminded me of the convention (outside python core) to name getters and setters so that they imply their returned type. Similarly for conversion methods like to_*()). But the name format, in my mind, implies that it only changes the contents of the str, rather than morphing its type.

The % example surprised me too, but it clicked for me when I realized % is a binary operator and not a method.

--Hobson (503) 974-6274 gh <https://github.com/hobson/> twtr <https://twitter.com/hobsonlane> li <https://www.linkedin.com/in/hobsonlane> g+ <http://plus.google.com/+HobsonLane/> so <http://stackoverflow.com/users/623735/hobs>

On Thu, May 18, 2017 at 7:25 AM, Random832 <random832 at fastmail.com> wrote:

On Thu, May 18, 2017, at 01:14, Hobson Lane wrote: > Because .format() is a method on an instantiated str object in e and > so > must return the same type

That it must return the same type is overstating the matter. Split returns a list (and, rather like %, the list is of unicode or str objects depending on the argument). Join will return a unicode object if any of the elements of the sequence are unicode. I was honestly surprised though to see that % returns unicode when formatting a unicode value, since my mental model of %s was more like {!s} - call str() on whatever object is at the given position in the right-hand argument. This kind of ad hoc implementation decision (format always returns str, other methods can return unicode, ljust/rjust refuse to accept a unicode character argument) is what Python 3 moved away from.

Python-Dev mailing list Python-Dev at python.org https://mail.python.org/mailman/listinfo/python-dev Unsubscribe: https://mail.python.org/mailman/options/python-dev/ hobsonlane%40gmail.com -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://mail.python.org/pipermail/python-dev/attachments/20170518/84e529a6/attachment.html>

More information about the Python-Dev mailing list