[Python-Dev] 2.4a2, and @decorators (original) (raw)

Michael Chermside mcherm at mcherm.com
Tue Aug 3 19:22:42 CEST 2004

James Knight writes:

However, it seems as if this restriction creates a new class of expression for no gain. It is true enough that most python expressions aren't useful to write after a @, but that's also true of a lot of other places an expression can be used (e.g. before a () of a function call. A list comprehension can never result in a callable object. An arithmetic operation usually won't.).

The only real necessary restriction on the @ operator is that its argument be callable and take a single argument. Many expressions could return a callable object. Why not let them? Is it really worth having a special case just to SyntaxError expressions that sometimes won't result in an appropriate callable? Things someone might want to do, ordered roughly from most reasonable to least reasonable ;) @foo().bar() @foo or bar @mydecorators['foo'] @lambda f: foo(f) or bar(f) Why disallow these forms? It seems quite difficult, especially, to explain why the first one does not, or should not, work.

Yeah... what he said.

Seriously, a well-designed programming language has very strong orthogonality. A few simple concepts should suffice. "an expression" is an existing production which is well-known to users and well understood. I agree that using complex expressions in a decorator leads to difficult-to-read code, but I would STILL like it to be possible, just so I don't have to remember (or teach) decorators as a special case.

-- Michael Chermside

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