[Python-Dev] Re: Guido's Magic Code was: inline sort option
Guido van Rossum
guido at python.org
Thu Oct 30 12:16:33 EST 2003
> Darn -- it WOULD be better in some cases if one could ONLY call
> a method on the class, NOT on an instance when the call would in
> any case ignore the instance. Calling dict.fromkeys(L3) is wonderful,
> the problem is that you can also call it on a dict instance, and THAT
> gets confusing. Similarly, calling list.sorted(iterable) is wonderful,
> but calling it on a list instance that gets ignored, L1.sorted(iterable),
> could perhaps be confusing.
Let's focus on making this an issue that one learns without much pain.
Given that the most common mistake would be to write a.sorted(), and
that's a TypeError because of the missing argument, perhaps we could
make the error message clearer?
Perhaps we could use a variant of classmethod whose __get__ would
raise the error, rather than waiting until the call -- it could do the
equivalent of the following:
def __get__(self, obj, cls):
if obj is not None:
raise TypeError, "class method should be called on class only!"
return classmethod.__get__(self, None, cls)
I don't want to make this behavior the default behavior, because I
can see use cases for calling a class method on an instance too,
knowing that it is a class method; otherwise one would have to write
the ugly x.__class__.foobar().
--Guido van Rossum (home page: http://www.python.org/~guido/)
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