building strings with variable input

Olaf Meyer nomail at
Mon Jan 12 16:55:42 CET 2004

Erik Max Francis wrote:

> Olaf Meyer wrote:
>>Especially if you have a lot of variable input it makes it hard to
>>the variables to the proper fields. From other scripting languanges
>>used to something like:
>>  $cmd = "$executable -start $startTime -end $endTime -dir $directory"
>>This makes it very easy to see how the string is actually built. You
>>dont't have to worry where which variables go.
>>Is there a similar way to do this in python?
> Sure:
> cmd = "%(executable)s -start %(startTime)s -end %(endTime)s -dir
> %(directory)s" % locals()
> There are also more expansive solutions such as YAPTU or EmPy.
> Note, however, that what you are trying to do (presuming you're passing
> this to os.system or something similar) is potentially a serious
> security risk.  If the values of the strings you are constructing the
> command line are not fully trustworthy, they can be easily manipulated
> to make your program execute arbitrary shell commands.

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)


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