how to join array of integers?

[Robert Kern]

Grant Edwards wrote:
> On 2007-09-15, Erik Jones <erik at myemma.com> wrote:
> 
>>>> print ''.join([str(i) for i in [1,2,3]])
>>> It's better to use generator comprehension instead of LC:
>>>
>>> ",".join(str(i) for i in [1, 2, 3])
>> Why is that?  That entire expression must be evaluated to obtain the  
>> result, so what is the advantage of using a generator comprehension  
>> v. a list comprehension?
> 
> The generator avoids creating the intermediate list -- it
> generates the intermediate values on the fly. For short
> sequences it probably doesn't matter much.  For a very long
> list it's probably noticable.

Not true. str.join() creates a list from the iterator if it is not already a
list or a tuple. In Objects/stringobject.c, look at string_join(); it calls
PySequence_Fast() on the argument. Looking in Objects/abstract.c, we see that
PySequence_Fast() short-circuits lists and tuples but builds a full list from
the iterable otherwise.

map() seems to reliably be the fastest option, and list comprehensions seem to
slightly edge out generator comprehensions if you do the timings.

-- 
Robert Kern

"I have come to believe that the whole world is an enigma, a harmless enigma
 that is made terrible by our own mad attempt to interpret it as though it had
 an underlying truth."
  -- Umberto Eco