idiom: concatenate strings with separator

[Christian Tanzer]

> Harald Kirsch <kirschh at lionbioscience.com> wote:
> 
> 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.

In general, the repeated string concatenation will be much slower --
each execution of `s = s + sep + y' copies `s' and discards the old
copy of `s'. For a few short strings it might not matter much, though.

BTW, timing the alternatives yourself is very easy -- see the standard
modules time and profile. Measuring performance is much more reliable
than guessing. Having usenetters guess might be even worse <wink>.

-- 
Christian Tanzer                                         tanzer at swing.co.at
Glasauergasse 32                                       Tel: +43 1 876 62 36
A-1130 Vienna, Austria                                 Fax: +43 1 877 66 92