[Python-Dev] Decorators: vertical bar syntax

[Bill Janssen]

GvR writes:
> Nevertheless I don't like to put decorators in the method body.  I
> think it has something to do with the fact that normally one thinks of
> the body contents as relevalt to "call-time" while decorators happen
> at "definition-time".
> 
> And before you bring up docstrings as a counterexample, yes, they
> should ideally have been designed to precede the method, too.

Perhaps another way to think about this is that there are statements
about properties of the function, method, or class which should
precede the implementation of the whatever-it-is?  That makes sense to
me.

But I'm less sure about the relative placement of the name of the
whatever versus statements about the properties of the whatever.  For
example, should the argument list also occur before the name of the
function?  In a perfect world, would Python have the syntax:

  def (param1, param2) funcname:
     ...

or perhaps:

  @args(param1, param2)
  def funcname:
     ...

In thinking about this, I find the argument made a day or two ago
about "cognitive binding" very powerful.  That is, you should state
the name of the thing you are defining before you start stating
properties of it, so that the reader has the opportunity to mentally
construct a tagged "bucket" to put those properties in.  This is
probably a useful thing for non-human tools, as well.

Perhaps that's one reason that arguments to a function almost
universally occur after the mention of the function name, in most
programming languages:

  def foo (arg1, arg2, ...)

So, by this principle, docstrings occur in the "right place", after
the function name but before the implementation.  Perhaps this is why
docstrings are so successful in Python.  Extending the principle to
decorators would mean that they should occur somewhere between the
function name and the function implementation.  All of the C, D, and E
variants in the Wiki seem to support this.  Perhaps one of them is the
right choice?

Bill