[Python-Dev] string-valued fget/fset/fdel for properties

Edward Loper edloper at gradient.cis.upenn.edu
Mon Nov 24 00:27:38 EST 2003

I was wondering if there would be any interest for adding a special
case for properties with string-valued fget/fset/fdel:

     - if fget is a string, then the getter returns the value of the
       member variable with the given name.
     - if fset is a string, then the setter sets the value of the
       member variable with the given name.
     - if fdel is a string, then the deleter deletes the member variable
       with the given name.

I.e., the following groups would be functionally equivalant:

     property(fget=lambda self: self._foo)
     property(fget=lambda self: getattr(self, '_foo'))

     property(fset=lambda self, value: setattr(self, '_foo', value))

     property(fdel=lambda self: delattr(self, '_foo'))

This change has 2 advantages:

     1. It's easier to read.  (In my opinion, anyway; what do other
        people think?)

     2. It's faster: for properties whose fget/fset/fdel are strings,
        we can avoid a function call (since the changes are implemented
        in c).  Preliminary tests indicate that this results in
        approximately a 3x speedup for a tight loop of attribute
        lookups.  (It's unclear how much of a speed increase you'd get
        in actual code, though.)

and one disadvantage (that I can think of):

     - It's one more special case to document/know.

This change shouldn't break any existing code, because there's
currently no reason to use string-valued fget/fset/fdel.

Does this change seem useful to other people?  Do the advantages
outweigh the disadvantage?  Or are there other disadvantage that I
neglected to notice?  If this seems like a useful addition, I'd be
happy to work on making a patch that includes test cases & doc


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