Re: self modifying code
- From: Ben C <spamspam@xxxxxxxxx>
- Date: 29 Apr 2006 22:43:50 GMT
On 2006-04-29, Robin Becker <robin@xxxxxxxxxxxxxxxxxxx> 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)
.
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