On Fri, 21 Nov 2008 13:25:45 -0800, Brentt wrote:
> I can't figure out why when I define a function, a variable
> (specifically a list) that I define and initialize in the argument
> definitions, will not initialize itself every time its called.
Because you haven't told the function to initialize the value every time
it's called. You are laboring under a misapprehension. Function default
values are created ONCE, when you define the function.
> So for
> example, when making a simple list of a counting sequence from num (a
> range list), if I call the function multiple times, it appends the
> elements to the list generated the times it was called before, even
> though the variable for the list is initialized in the argument
> definitions.
No it isn't. You need to re-set your thinking, that's not what Python
does. Try this:
def expensive():
# simulate an expensive function call
import time
time.sleep(30)
return time.time()
def parrot(x=expensive()):
return x
The expensive call is made once only. If you want it made every time, you
have to explicitly make that call every time:
def parrot(x=None):
if x is None:
x = expensive()
return x
For bonus marks, predict the behaviour of this:
def spam():
def ham(x=expensive()):
return x
return ham()
--
Steven
--
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