[Python-ideas] Dunder method to make object str-like

MRAB python at mrabarnett.plus.com
Thu Apr 7 10:11:09 EDT 2016

On 2016-04-07 14:04, Chris Angelico wrote:
> This is a spin-off from the __fspath__ discussion on python-dev, in
> which a few people said that a more general approach would be better.
> Proposal: Objects should be allowed to declare that they are
> "string-like" by creating a dunder method (analogously to __index__
> for integers) which implies a loss-less conversion to str.
> This could supersede the __fspath__ "give me the string for this path"
> protocol, or could stand in parallel with it.
> Obviously str will have this dunder method, returning self. Most other
> core types (notably 'object') will not define it. Absence of this
> method implies that the object cannot be treated as a string.
> String methods will be defined as accepting string-like objects. For
> instance, "hello"+foo will succeed if foo is string-like.
> Downside: Two string-like objects may behave unexpectedly - foo+bar
> will concatenate strings if either is an actual string, but if both
> are other string-like objects, depends on the implementation of those
> objects.
> Bikeshedding:
> 1) What should the dunder method be named? __str_coerce__? __stringlike__?
> 2) Which standard types are sufficiently string-like to be used thus?
> 3) Should there be a bytes equivalent?
> 4) Should there be a format string "coerce to str"? "{}".format(x) is
> equivalent to str(x), but it might be nice to be able to assert that
> something's stringish already.
> Open season!

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