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Portable code: __import__ demands different string types between 2 and 3

Ethan Furman ethan at stoneleaf.us
Mon Dec 15 20:49:14 EST 2014 
On 12/15/2014 05:36 PM, Ben Finney wrote:
> 
> That's not the issue at all. I know how to declare a literal such that
> it is Unicode in Python 2 and Python 3 (that's what the ‘from __future__
> import unicode_literals’ does).
> 
> Rather, the problem is ‘__import__’ having incompatible expectations:
> the ‘fromlist’ parameter's items must be bytes in Python 2, and must be
> Unicode in Python 3.

Ah.  Well, then you do not want the `unicode_literals` import or it won't be bytes in Python 2 (as I'm sure you know).


> The same parameter value can't satisfy both those requirements in a
> single 2-and-3 compatible code base, without either using the
> bytes-and-text ambiguity of ‘str’, or some kludge over-riding a simple
> ‘__import__’ call. Both of those are ugly and make for buggy code.

If this is for a large(ish) application, make one module with stuff that needs the ambiguity to work correctly.  Comment
the heck out of it.  ;)


> I'm increasingly of the opinion this is a subtle bug in ‘__import__’
> that should be fixed instead of worked around.

Of course.  But you'll still need to work around it for previous versions, unless you can say you only support 2.7.10+
(maybe 2.7.9+ if it gets fixed quick enough).

> But it will likely be rejected because the documentation advises against using ‘__import__’.

Functions that should accept str but barf on unicode have a tendency to get fixed.

--
~Ethan~

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