String building using join

[Emile van Sebille]

On 1/2/2011 9:43 AM gervaz said...
> On 31 Dic 2010, 16:43, Emile van Sebille<em... at fenx.com>  wrote:
>> On 12/31/2010 7:22 AM gervaz said...
>>
>>
>>
>>
>>
>>> 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
>>> ...
>>>>>> t1 = Test("hello", None)
>>>>>> t2 = Test(None, "ciao")
>>>>>> t3 = Test("salut", "hallo")
>>>>>> t = [t1, t2, t3]
>>
>>>>>> prg(t)
>>> 'hello\nciao\nsalut\nhallo\n'
>>
>>> The idea would be create a new list with the values not None and then
>>> use the join function... but I don't know if it is really worth it.
>>> Any hint?
>>
>>>>>> def prg2(l):
>>
>>               return "\n".join([x for x in l if x])
>>
>> Emile
>>
>>
>>
>>> ...     e = []
>>> ...     for x in l:
>>> ...         if x.v1 is not None:
>>> ...             e.append(x.v1)
>>> ...         if x.v2 is not None:
>>> ...             e.append(x.v2)
>>> ...     return "\n".join(e)
>>> ...
>>>>>> prg2(t)
>>> 'hello\nciao\nsalut\nhallo'
>>
>>> Thanks, Mattia- Nascondi testo citato
>>
>> - Mostra testo citato -- Nascondi testo citato
>>
>> - Mostra testo citato -
>
> Sorry, but it does not work

Oh -- you want a working solution, not a hint?  OK.

class Test:
      def __init__(self, v1, v2):
          self.v1 = v1
          self.v2 = v2


t1 = Test("hello", None)
t2 = Test(None, "ciao")
t3 = Test("salut", "hallo")
t = [t1, t2, t3]


"\n".join([y for x in t for y in [x.v1,x.v2] if y])

Emile

>
>>>> def prg3(l):
> ...     return "\n".join([x for x in l if x])
> ...
>>>> prg3(t)
> Traceback (most recent call last):
>    File "<stdin>", line 1, in<module>
>    File "<stdin>", line 2, in prg3
> TypeError: sequence item 0: expected str instance, Test found