String building using join

Tue Jan 4 15:36:56 EST 2011

gervaz <gervaz at gmail.com> writes:
> Hi all, I would like to ask you how I can use the more efficient join
> operation in a code like this:
>>>>> class Test:
> ... def __init__(self, v1, v2):
> ... self.v1 = v1
> ... self.v2 = v2
> ...

>>>> def prg(l):
> ... txt = ""
> ... for x in l:
> ... if x.v1 is not None:
> ... txt += x.v1 + "\n"
> ... if x.v2 is not None:
> ... txt += x.v2 + "\n"
> ... return txt
> ...

You can change the prg() function above slightly to make it a generator
function:
def genprg(l):
 for x in l:
 if x.v1 is not None:
 yield x.v1
 if x.v2 is not None:
 yield x.v2
Then you can rewrite prg using join:
def prg(l):
 return '\n'.join(genprg(l))
This way you save yourself from creating a list. I know this is not the
one liner that others have suggested but it shows a general way of
transforming a piece of code in order to make use of generator functions.
-- 
Arnaud