What I can't find an explanation for is why str.join() doesn't automatically call str() on its arguments
I don't really like that idea for the reasons others have stated. But a related and (IMHO) more Pythonic idea would be to allow arbitrary objects to be str.join()ed if they use __radd__ to allow concatenation with strings. This would be consistent with how the + operator behaves:
Python 2.4 (#2, Jan 8 2005, 20:18:03) [GCC 3.3.5 (Debian 1:3.3.5-5)] on linux2 Type "help", "copyright", "credits" or "license" for more information. >>> class Foo(object): ... def __radd__(self, other): ... if isinstance(other, basestring): ... return other + str(self) ... def __str__(self): ... return 'Foo()' ... >>> 'foo:' + Foo() 'foo:Foo()' >>> ''.join(['foo', Foo()]) Traceback (most recent call last): File "<stdin>", line 1, in ? TypeError: sequence item 1: expected string, Foo found -- http://mail.python.org/mailman/listinfo/python-list
