On 2006-04-29, Robin Becker <[EMAIL PROTECTED]> wrote:
> When young I was warned repeatedly by more knowledgeable folk that self
> modifying code was dangerous.
>
> Is the following idiom dangerous or unpythonic?
>
> def func(a):
> global func, data
> data = somethingcomplexandcostly()
> def func(a):
> return simple(data,a)
> return func(a)
It looks quite clever (a bit too clever ... :)
> It could be replaced by
>
> data = somethingcomplexandcostly()
> def func(a):
> return simple(data,a)
>
> but this always calculates data.
Why not just:
data = None
def func(a):
global data
if not data:
data = somethingcomplexandcostly()
return simple(data, a)
Or nicer to use a "singleton" perhaps than a global, perhaps something
like this:
class Func(object):
exists = False
def __init__(self):
assert not Func.exists
Func.exists = True
self.data = None
def simple(self, a):
assert self.data is not None
# ... do something with self.data presumably
return something
def __call__(self, a):
if self.data is None:
self.data = somethingcomplexandcostly()
return self.simple(a)
func = Func()
func(a)
--
http://mail.python.org/mailman/listinfo/python-list
