- E04 - Leadership! Google, Guido van Rossum, PSF

Alex Martelli aleax at mail.comcast.net
Wed Jan 4 17:02:26 CET 2006


Ilias Lazaridis <ilias at lazaridis.com> wrote:
   ...
> >>   attr_accessor :name, :age
   ...
> I would need this python "attr_accessor", to showcase that python is 
> capable to do it (even if the usage seems irrational/redundant).

The code for it was in one of my previous posts, in more than one form,
but here it is again, more or less:

def add_silly_attr_accessor_to_a_class(klass, name):
   def get(self, name): return getattr(self, '_'+name)
   def set(self, name, value): return setattr(self, '_'+name, value)
   setattr(klass, name, property(get, set))

to be used as in:

add_silly_attr_accessor_to_a_class(Talker, 'name')
add_silly_attr_accessor_to_a_class(Talker, 'age')

outside of the body of Talker.  If you'd rather have it used INSIDE the
body of Talker, then:

def make_silly_attr_accessor(name):
   def get(self, name): return getattr(self, '_'+name)
   def set(self, name, value): return setattr(self, '_'+name, value)
   return property(get, set)

to be used as in:

class Talker(object):
  age = make_silly_attr_accessor('age')
  name = make_silly_attr_accessor('name')

Finally, you could choose to use a decorator syntax instead:

def silly_attr_accessor_via_decorator(f):
   name = '_'+f.__name__
   def get(self, name): return getattr(self, '_'+name)
   def set(self, name, value): return setattr(self, '_'+name, value)
   return property(get, set)

to be used as in:

class Talker(object):
  @silly_attr_accessor_via_decorator
  def name(): pass
  @silly_attr_accessor_via_decorator
  def age(): pass

The latter is arguably a stretching of the concept of decorator, which
is meant to be a nice syntax for a higher-order-function (taking a
function as its argument and returning another function built by
modifying the argument one) -- here we're only using the *name* of the
"function" (name or age) and ignoring the object entirely (which is why
in the example use I'm defining the ``functions'' as empty, using the
no-op statement ``pass'').  Still, some people believe there is mystical
and magical power in having special syntax for something rather than
using perfectly normal, general, and existing syntax for the purpose;
such syntax-obsessed people will no doubt be more impressed by seeing
the "special syntax" in use, than by ordinary, bread-and-butter
closures, properties and assignment statements...;-)


Alex



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