Uwe Mayer wrote:
Hi,
I've been looking into ways of creating singleton objects. With Python2.3 I
usually used a module-level variable and a factory function to implement
singleton objects.
With Python2.4 I was looking into decorators. The examples from PEP 318
http://www.python.org/peps/pep-0318.html#examples
don't work - AFAIK because:
- you cannot decorate class definitions (why was it left out?)
- __init__ must return None
However, you can use the decorator:
def singleton(f):
instances = {}
def new_f(*args, **kwargs):
if (f not in instances):
instances[f] = f(*args, **kwargs)
return instances[f]
new_f.func_name = f.func_name
new_f.func_doc = f.func_doc
return new_f
with a class that overwrites the __new__ methof of new-style classes:
class Foobar(object):
def __init__(self):
print self
@singleton
def __new__(self):
return object.__new__(Foobar)
Is this particularly ugly or bad?
Seems a little confoluted. Why can't you just use something like:
class Singleton(object):
def __new__(cls, *args, **kwargs):
try:
return cls.__instance__
except AttributeError:
instance = cls.__instance__ = super(Singleton, cls).__new__(
cls, *args, **kwargs)
return instance
class Foobar(Singleton):
def __init__(self):
print self
?
STeVe
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