building strings with variable input

Tim Roberts timr at
Wed Jan 14 08:31:31 CET 2004

Olaf Meyer <nomail at> wrote:
>I just found out another way ;-) Using the locals() has the disadvantage 
>that I cannot use more complex variable parameters (e.g. certain values 
>of a dictionary). The following works well:
>cmd = (executable + " -start " + startTime + " -end " + endTime +
>        " -dir " + options.dir)

Yes, that works, but you should bear in mind that it is slower than the %s
option.  The "+" operations are all separate interpreter steps, while the
"%" operation is done in C.

At least, it was that way when I asked this same question several years
ago.  If it has changed, I'm sure someone will point out my error.

Sometimes, it can make sense to write it this way:

  cmd = ' '.join((
         "-start", startTime,
         "-end", endTime,
         "-dir", options.dir
- Tim Roberts, timr at
  Providenza & Boekelheide, Inc.

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