Implicit conversion to str in str.join method?

[Kirill Balunov]

Currently `str.join` raises `TypeError` if there are any non-string values
in iterable, including `bytes` objects. Is it an awful idea to implicitly
_cast_ elements in iterable to their `str` or `repr` representation? Was
this question adressed before?

As for me there are two valid points: On one hand "Explicit is beter than
implicit" and on the other "Practicality beats purity". May be I'm the only
one who finds that it is rather boring to write somehting like:

    ", ".join(str(i) for i in iterable)

when iterable contains non-string values, instead of:

    ", ".join(iterable)

I don't know how much overhead will yield for the case when iterable
contains only strings...and if it is possible to optimize this case. This
change is backward compatible, but as I wrote above, it can be perceived
badly and yield a huge overhead for general case that it is not even worth
discussing. What do you think?

With kind regards,
-gdg