Possible PEP: Improve classmethod/staticmethod syntax

Kevin Smith Kevin.Smith at sas.com
Tue Jun 3 22:45:18 CEST 2003


The current way of declaring a method to be a class method or a static 
method leaves much to be desired.  While it is flexible in the sense 
that new types of method modifiers can be created without any 
syntactical backwards incompatibilities, it just isn't that user-
friendly (and, in turn, not Pythonic).

A new proposed syntax for method modifiers is as follows:

    def classmethod foo(cls):
        <code goes here>

    def staticmethod bar():
        <code goes here>

An optional keyword is added before the function name itself.  This 
keyword is simply a reference to a function that will be applied to the 
method once the method is compiled.  In essence, the above syntax 
expands to:

    def foo(cls):
        <code goes here>
    foo = classmethod(foo)

    def bar():
        <code goes here>
    bar = staticmethod(bar)

The motivation here isn't so much terseness as it is understandability.  
The call to classmethod() or staticmethod() in this short example is 
very close to the original 'def', so it is easy to follow.  However, if 
the method is any more than about 15 lines of code, the transformation 
to a class method or static method isn't obvious.  The proposed syntax 
puts the class/static method conversion at the point of definition where 
it makes the most sense.  This placement also makes it easier for 
documentation generators or IDEs to give visual cues when class or 
static methods are used.

I am not familiar with how the classmethod() or staticmethod() functions 
actually work and if they would support this, but a possible extension 
to the original syntax would be to add multiple modifiers before the 
method name.

    def protected classmethod foo(cls):
        <code goes here>

This would expand to:

    def foo(cls):
        <code goes here>
    foo = protected(classmethod(foo))
  
What all this boils down to is that any function that can return a new 
function reference (i.e. classmethod()/staticmethod()/protected()) when 
given a function reference (i.e. foo/bar) could be used as a modifier.  
If it is technically feasible, it would be nice if multiple modifiers 
were allowed.  The proposed syntax does not cause any backwards 
incompatibilities since it is simply uses the existing function 
modifiers and they can still be used the way they were originally 
designed.

-- 
Kevin Smith
Kevin.Smith at sas.com




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