On Sun, 02 May 2010 05:08:53 +1000, Lie Ryan wrote: > On 05/01/10 11:16, Steven D'Aprano wrote: >> On Fri, 30 Apr 2010 12:34:34 -0400, D'Arcy J.M. Cain wrote: >> >> In practice though, I think that's a difference that makes no >> difference. It walks like an operator, it swims like an operator, and >> it quacks like an operator. >> >> > Nope it's not. A full-time operator in python have a reflected version > (e.g. __radd__), which dot does not have.
What are the reflected versions of __eq__ and __ne__ (binary == and != operators)? And __neg__, __pos__ and __inv__ (for the unary - + and ~ operators)? And the three-argument form of __pow__ for power(1, 2, x)? > And Python's object system > makes it that the argument to __getattr__ is always a string even though > there might be a valid variable that corresponds to it: That is nothing to do with the object system, it is related to the semantics of Python syntax. a.b doesn't mean "apply the binary dot operator to arguments a and b". It is syntactic sugar for "look for an attribute named 'b' on object a". As such, the operands that __getattr__ receives are the object a and the *name* b (implemented as a string). Also, the implementation of attribute lookup is quite complex, with all sorts of special cases and optimizations. > a = MyClass() > b = MyClass() > print a . b > > I've often wanted to figure out a way to (ab)use python's dot operator > for function composition (i.e. f.g(x) ==> f(g(x)) ). There's no way to > do it, not without being way too hackish. That's a good example of where the difference does make a difference. -- Steven -- http://mail.python.org/mailman/listinfo/python-list
