best way of testing a program exists before using it?

[Steve Holden]

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
> 
Except that the fname will then have to be a ".exe" on Windows and not 
on Unix.

regards
  Steve
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