[Python-ideas] Add list.join() please

Chris Barker chris.barker at noaa.gov
Tue Jan 29 15:49:19 EST 2019

A couple notes:

On Tue, Jan 29, 2019 at 5:31 AM Jamesie Pic <jpic at yourlabs.org> wrote:

> can you clarify the documentation
> topic you think should be improved or created ? "Assembling strings"

I would think "assembling strings", though there is a lot out there already.

> or "inconsistencies between os.path.join and str.join" ?

well, if we're talking about moving forward, then the Path object is
probably the "right" way to join paths anyway :-)

a_path / "a_dir" / "a_filename"

But to the core language issue -- I started using Python with 1.5.* and
back then join() was in the string module (and is there in 2.7 still)

And yes, I did expect it to be a list method...

Then it was added as a method of the string object.

And I thought THAT was odd -- be really appreciated that I didn't need to
import a module to do something fundamental.

But the fact is, that joining strings is fundamentally a string operation,
so it makes sense for it to be there.

In earlier py2, I would have thought, maybe it should be a list method --
it's pretty darn common to join lists of strings, yes? But what about
tuples? Python was kind of all about sequences -- so maybe all sequences
could have that method -- i.e part of the sequence ABC.

But with > py3k, Python is more about iterables than sequences -- and join
(and many other methods and functions) operate on any iterable -- and this
is a really good thing.

So add join to ALL iterables? That makes little sense, and really isn't
possible -- an iterable is something that conforms to the iterator protocol
-- it's not a type, or even an ABC.

So in the end, join really does only make sense as string method.

Or Maybe as a built in -- but we really don't need any more of those.

If you want to argue that str.join() should take multiple arguments, like
os.path.join does, then, well we could do that -- it currently takes one
and only one argument, so it could be extended to join multiple arguments
-- but I have hardly ever seem a use case for that.

The mistake I'm still doing after 10 years of Python

hmm -- I've seen a lot of newbies struggle with this, but haven't had an
issue with it for years myself.

>     >>> '/'.join('some', 'path')
>     TypeError: join() takes exactly one argument (2 given)

pathlib aside, that really isn't the right way to join paths .....
os.path.jon exists for a (good) reasons. One of which is this:

In [22]: os.path.join("this/", "that")
Out[22]: 'this/that'



Christopher Barker, Ph.D.

Emergency Response Division
NOAA/NOS/OR&R            (206) 526-6959   voice
7600 Sand Point Way NE   (206) 526-6329   fax
Seattle, WA  98115       (206) 526-6317   main reception

Chris.Barker at noaa.gov
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.python.org/pipermail/python-ideas/attachments/20190129/306e0cfa/attachment.html>

More information about the Python-ideas mailing list