I sometimes inadvertently create a new attribute on an object rather
update a value bound to an existing attribute. For example:
In [5]: class some_class(object):
...: def __init__(self, a=None):
...: self.a = a
...:
In [6]: c = some_class(a=1)
In [7]: c.a
Out[7]: 1
In [8]: c.A = 2
I meant to update c.a but I created a new c.A. I make this mistake
probably hourly.
I suspect adding attributes at run time can be a beautiful thing, but in
this particular instance, I'm only using this feature to hurt myself.
I wrote a simple class that will warn me when I make this mistake in the
future:
import warnings
class C(object):
warn_on_new_attributes = True
standard_attributes = []
def __setattr__(self, name, value):
if self.warn_on_new_attributes \
and name is not 'warn_on_new_attributes' \
and name not in self.standard_attributes:
warnings.warn("%s has no standard attribute %s."
% (self.__class__.__name__, name))
self.__dict__[name] = value
class C1(C):
standard_attributes = ['a1', 'a2']
class C2(C):
warn_on_new_attributes = False
# Do some simple testing.
c11 = C1()
c11.a1 = 1
c11.a2 = 2
c11.a3 = 3
c11.a4 = 4
# Disable warnings for this instance.
c12 = C1()
c12.warn_on_new_attributes = False
c12.a1 = 1
c12.a2 = 2
c12.a3 = 3
c12.a4 = 4
c11.a5 = 5
# Use an object that has warnings disabled by default.
c2 = C2()
c2.a1 = 1
c2.a2 = 2
c2.a3 = 3
c2.a4 = 4
# enable warnings for this object.
c2.warn_on_new_attributes = True
c2.a1 = 1
c2.a5 = 5
All comments are welcome. Is there a better way of implementing the
above class, OR, is this approach generally wrong-headed? Am I the only
one that makes this mistake?
TIA
--
A better way of running series of SAS programs:
http://overlook.homelinux.net/wilsonwiki/SasAndMakefiles
--
http://mail.python.org/mailman/listinfo/python-list
