stylistic question -- optional return value
wurmy at earthlink.net
Wed Aug 28 20:32:09 CEST 2002
Andrew Koenig wrote:
> Suppose I have a function that sometimes returns one value and sometimes
> returns two. What's the cleanest way to define such an interface?
In general, it may be better to use two separate functions, aside... the
"sometimes it returns A and something it returns B" is usually not a good idea.
However, I don't know the exact situation.
> Another possibility is to return either (x, None) or (x, y). Now
> it is easy to extract x from the compound result. However,
> that strategy removes None from the set of permissible values for y.
> Yet another possibility is to return (False, x) or (True, x, y).
> Now x is in a common position, so retrieving it is straightforward.
> However, I can obtain the same information content by returning
> (x,) or (x, y). However, I can easily imagine people becoming
> confused by 1-tuples.
> What is the most Pythonic way of solving this problem?
I can think of some yucky solutions, like writing a special class that has one
or two attributes depending on what you return. That can hardly be called
"Pythonic", though. :-/
A bit better would be, using a special instance to signify an "empty slot",
like you use None in your example above:
class Null: pass
Null = Null()
Functions can now return (x, y) or (x, Null). The latter cannot be confused
with (x, y) where y is None.
Still, I believe that rewriting the function (or splitting it up) might be a
better idea. <0.3 wink>
# decode for email address ;-)
The Pythonic Quarter:: http://www.awaretek.com/nowak/
More information about the Python-list