Variables and none?
steve at holdenweb.com
Fri Jan 20 22:55:33 EST 2006
Ivan Shevanski wrote:
> Alright first of all I'd like to say I'm a python noob.
Welcome to c.l.py.
> Now that thats over with, heres what I'd like to know about. Is there a
> python way to detect if a variable exsists? Say I had a program that
> needed a certain variable to be set to run and the variable was not
> found when it came time to use it. . .Would I just have to catch the
> error, or could I have python look for the variable beforehand?
The usual way to do this is to catch the error.
If you can access the namespace of interest (say it's an instance of
some class) then you can use hasattr() to answer the question, but
catching the exception is the generic way to do it.
However, across a function call interface the usual way to allow values
to not be provided by the caller is to provide a default value for the
argument, such as
def f(x, something=2):
That way if the caller just says
that's equivalent to
but it's also possible to say
both of which are equivalent. Does this help at all?
Steve Holden +44 150 684 7255 +1 800 494 3119
Holden Web LLC www.holdenweb.com
PyCon TX 2006 www.python.org/pycon/
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