[Python-Dev] decorators: If you go for it, go all the way!!! :) (original) (raw)

alex_nanou at cs.msu.su alex_nanou at cs.msu.su
Thu Aug 26 12:58:30 CEST 2004

the inability to decorate anything but a function, is quite a limitation, though I must agree that decorating classes is not such a common task, but using the syntax to decorate attributes would indeed prove useful (in both the readability department and the uniformity of code)..

here is an example we use quite often: ---cut--- import time import sys

def intonly(obj=0, doc=None): ''' intonly(int) -> descriptor

the resulting descriptor will prevent both the deletion of the
attribute and assignments of any value other than ints.
'''
if type(obj) is not int:
    raise TypeError, 'value must be int (got: %s)' % obj

f_locals = sys._getframe(1).f_locals

# name the attr (I know this is ugly ^_^ )
while True:
    name = '_priv_' + str(int(time.time()*10**8))
    if name not in f_locals:
        f_locals[name] = obj
        break

# the descriptor reader function...
def read(self):
    return getattr(self, name)

# the descriptor writer...
def write(self, val):
    if type(val) is not int:
        raise TypeError, 'value must be int (got: %s)' % val
    setattr(self, name, val)

# now create the descriptor and return it...
return property(read, write, doc=doc)

--uncut--

and here are a couple of usage examples: the desired decorator syntax: ---cut--- class A(object): @intonly i = 123

--uncut--

the current usage syntax: ---cut--- class A(object): i = intonly(123)

--uncut--

// sorry if I bring this up agen! :) thanks!

                                       Best Regards...
                                                  Alex.

More information about the Python-Dev mailing list