Why doesn't join() call str() on its arguments?

[Jeff Shannon]

Leo Breebaart wrote:

> What I can't find an explanation for is why str.join() doesn't
> automatically call str() on its arguments [...]

> [...] Presumably there is some
> counter-argument involved, some reason why people preferred the
> existing semantics after all. But for the life of me I can't
> think what that counter-argument might be...

One possibility I can think of would be Unicode.  I don't think that 
implicitly calling str() on Unicode strings is desirable.  (But then 
again, I know embarrassingly little about unicode, so this may or may 
not be a valid concern.)

Of course, one could ensure that unicode.join() used unicode() and 
str.join() used str(), but I can conceive of the possibility of 
wanting to use a plain-string separator to join a list that might 
include unicode strings.  Whether this is a realistic use-case is, of 
course, a completely different question...

Jeff Shannon
Technician/Programmer
Credit International