idiom: concatenate strings with separator

[M.-A. Lemburg]

Harald Kirsch wrote:
> 
> Recently I started using code like this
> 
> l = []
> for x in somethings:
>   y = massage(x)
>   l.append(y)
> 
> return string.join(y, my_favorite_separator)
> 
> to produce strings made of substrings separated by something. Note
> that with immediate string concatenation its hard to avoid the
> separator either in front or at the end of the produced string.
> 
> Nevertheless I wonder if something like
> 
> s = ""
> sep = ""
> for x in somethings:
>   y = massage(x)
>   s = s + sep + y
>   sep = my_favorite_separator
> 
> return s
> 
> is faster or uses less memory than the previous solution.

The fastest and most memory efficient solution is probably
using cStringIO:

import cStringIO
sep = "-"
temp = cStringIO.StringIO()
write = temp.write
for x in items:
    write(sep)
    write(x)
temp.seek(len(sep))
return temp.read()

PS: But Lutz Ehrlich would have told you that too ;-)

-- 
Marc-Andre Lemburg
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