Understand "better" as a quicker, elegant and readable.
I have two strings (a and b) that could be null or not. And I want concatenate them separated by a hyphen only if both are not null:
a - b
a (if b is null)
b (where a is null)
# Concatenates a and b with ' - ' or Coalesces them if one is None
'-'.join([x for x in (a,b) if x])
Edit
Here are the results of this algorithm (Note that None will work the same as ''):
>>> '-'.join([x for x in ('foo','bar') if x])
'foo-bar'
>>> '-'.join([x for x in ('foo','') if x])
'foo'
>>> '-'.join([x for x in ('','bar') if x])
'bar'
>>> '-'.join([x for x in ('','') if x])
''
*Also note that Rafael's assessment, in his post below, only showed a difference of .0002 secs over a 1000 iterations of the filter method, it can be reasoned that such a small difference can be due to inconsistencies in available system resources at the time of running the script. I ran his timeit implementation over several iteration and found that either algorithm will be faster about 50% of the time, neither by a wide margin. Thus showing they are basically equivalent.