On 06/30/2010 11:39 AM, Stef Mientki wrote:
hello,
I've lot of functions that returns their result in some kind of tuple
/ list / array,
and if there is no result, these functions return None.
Now I'm often what to do something if I've more than 1 element in the
result.
So I test:
if len ( Result ) > 1 :
But to prevent exceptions, i've to write ( I often forget)
if Result and ( len ( Result ) > 1 ) :
So I wonder why len is not allowed on None
and if there are objections to extend the len function .
thanks,
Stef Mientki
Because the natural interpretation of len only makes sense for concepts
such as a container or collection. The value None is no such thing.
Assigning a meaning to len(None) begs the question of meanings for
len(True), len(False), len(3.14), len(sys), ... This is a slippery
slope, best avoided.
But there are solutions:
1. Have your functions return [] or () or whatever. If they are to
return a list, and the list may be empty, [] is correct.
2. If you insist on a function returning a list sometimes and other
values at other times (such as None), then be prepared to write your
code which uses the result with test to determine which type was
returned. Fortunately that's not hard, as your one example shows.
3. Create a test function Empty(Result) which does what you want
returning a boolean and write your tests as:
if Empty(Result): ...
Gary Herron
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