On Mon, May 06, 2002, Guido van Rossum wrote:
>Aahz:
>>
>> Should file(fileinput.input()) work? Currently it raises an
>> exception because fileinput.input() returns neither a string nor a
>> buffer object.
>
> What on earth would you want it to do? It doesn't seem to make any
> sense to me.
Well, if it should work, it should return the FileInput instance (i.e.
return self). On thinking further, I'm going to use a slightly
different question divorced from my current problem:
What should list(UserList()) return? What about
class myList(list):
pass
l = list(myList())
I suppose this question is related to PEPs 245/246. The broader
question is, what should a constructor return when called on a related
object or subclass?
Getting back to my specific example, I've got this function:
def grep(f, regex):
f = file(f)
regex = re.compile(regex)
for line in f:
if regex.search(line):
yield line
I was originally passing in file handles or filenames, demonstrating to
the students that calling a constructor on an existing object returns
that object if it doesn't need to do any real work. Alex suggested that
I use fileinput.input(), whereupon my function blew up.
The meta question is, what kind of programming style do we want to push?
More smarts on top or bottom?
--
Aahz (aahz@pythoncraft.com) <*> http://www.pythoncraft.com/
See me at OSCON! I'm teaching Python for [Perl] Programmers, a fast intro
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