best way of testing a program exists before using it?

[Hari Sekhon]

Rob Wolfe wrote:
> Hari Sekhon wrote:
>   
>> I am writing a wrapper to a binary command to run it and then do
>> something with the xml output from it.
>>
>> What is the best way of making sure that the command is installed on the
>> system before I try to execute it, like the python equivalent of the
>> unix command "which"?
>>
>> Otherwise I'd have to do something like:
>>
>> if os.system('which somecommand') != 0:
>>     print "you don't have %s installed" % somecommand
>>     sys.exit(1)
>>
>> I know that isn't portable which is why a python solution would be
>> better (although this will run on unix anyway, but it'd be nice if it
>> ran on windows too).
>>     
>
> IMHO this is pretty portable:
>
>   
>>>> def is_on_path(fname):
>>>>         
> ...     for p in os.environ['PATH'].split(os.pathsep):
> ...             if os.path.isfile(os.path.join(p, fname)):
> ...                     return True
> ...     return False
>
> HTH,
> Rob
>
>   

That works well and is portable, fits nicely. I was actually curious if 
somebody already came across this and perhaps put a func like this in 
the standard modules...

Thanks.

-h

-- 
Hari Sekhon

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