Python as a scripting language. Alternative to bash script?
in [Python]
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From: Dave Pawson on 28 Jun 2010 07:48 I've a fairly long bash script and I'm wondering how easy it would be to port to Python. Main queries are: Ease of calling out to bash to use something like imageMagick or Java? Ease of grabbing return parameters? E.g. convert can return both height and width of an image. Can this be returned to the Python program? Can Python access the exit status of a program? I'd prefer the advantages of using Python, just wondering if I got so far with the port then found it wouldn't do something? Has anyone made this comparison please? TIA -- Dave Pawson XSLT XSL-FO FAQ. Docbook FAQ. http://www.dpawson.co.uk
From: Benjamin Kaplan on 28 Jun 2010 10:58 On Mon, Jun 28, 2010 at 4:48 AM, Dave Pawson <dave.pawson(a)gmail.com> wrote: > I've a fairly long bash script and I'm wondering > how easy it would be to port to Python. > > Main queries are: > Ease of calling out to bash to use something like imageMagick or Java? Easiest way is os.system, most flexible way is subprocess.Popen. > Ease of grabbing return parameters? E.g. convert can return both > height and width of an image. Can this be returned to the Python program? How does a program return anything other than an exit code? Subprocess allows you to read the program's stdout if that's what you're looking for. In the case of ImageMagick, you can use a Python wrapper to the library instead of calling the program from the command line, and then you can get all the return values you want. > Can Python access the exit status of a program? proc = subprocess.Popen(args) retcode = proc.wait() There's a shortcut of retcode = subprocess.call(args), but that doesn't give you access to stdout, just the return code. > > I'd prefer the advantages of using Python, just wondering if I got > so far with the port then found it wouldn't do something? > If there's anything it can't do that bash can, you can always just call the shell command. > Has anyone made this comparison please? > If you already have a working shell script, it's probably not worth your time. But if you've having trouble getting bash to cooperate, it's not that difficult to rewrite a shell script in Python. > TIA > > -- > Dave Pawson > XSLT XSL-FO FAQ. > Docbook FAQ. > http://www.dpawson.co.uk > -- > http://mail.python.org/mailman/listinfo/python-list >
From: D'Arcy J.M. Cain on 28 Jun 2010 11:29 On Mon, 28 Jun 2010 12:48:51 +0100 Dave Pawson <dave.pawson(a)gmail.com> wrote: > I've a fairly long bash script and I'm wondering > how easy it would be to port to Python. That's too big a question without seeing more of what your script does. I will try to suggest some direction though. First, if you have a complicated bash script that works, the best choice may be to just leave it alone. Think about Python for your next project instead. > Main queries are: > Ease of calling out to bash to use something like imageMagick or Java? You don't need to call bash to call an external program. Check out the subprocess module. If you do need a shell to simplify calling a program (environment and wild card expansione.g.) don't call bash. Just use a basic sh. You won't be using the bash control structures so keep to whatever is supplied by your OS. If that turns out to be bash anyway then no harm. Another option is to write small Python scripts that you can call from your bash script. You can even create them in your bash script. Here is a silly example. uc="import sys s = sys.argv[1] print s.upper() " .... echo -n "Upper case of $SOMESTRING is "; python -c "$uc" $SOMESTRING > Ease of grabbing return parameters? E.g. convert can return both > height and width of an image. Can this be returned to the Python program? Just to set the terminology straight, a parameter is what you call the function with. The return value is what it returns. The program output is what it emits (prints.) Programs return an integer value. This is also called the exxit status. On success this is 0 but can be otherwise on failure. You can use this, for example, with diff to determine if two files differ when you don't care how they differ. What you want is the output of the program. For this you need to capture the output and parse it. Look at the subprocess module. -- D'Arcy J.M. Cain <darcy(a)druid.net> | Democracy is three wolves http://www.druid.net/darcy/ | and a sheep voting on +1 416 425 1212 (DoD#0082) (eNTP) | what's for dinner.
From: Dave Pawson on 28 Jun 2010 12:08 Thanks for the replies (and Benjamin). Not met with the subprocess idea. On 28 June 2010 16:29, D'Arcy J.M. Cain <darcy(a)druid.net> wrote: >> Main queries are: >> Ease of calling out to bash to use something like imageMagick or Java? > > You don't need to call bash to call an external program. Â Check out the > subprocess module. Will do. Â If you do need a shell to simplify calling a > program (environment and wild card expansione.g.) don't call bash. I can get what I want from Python. No envars needed. >> Ease of grabbing return parameters? E.g. convert can return both >> height and width of an image. Can this be returned to the Python program? > > Just to set the terminology straight, a parameter is what you call the > function with. Â The return value is what it returns. Â The program > output is what it emits (prints.) My bad. I mean return values, though I do want program out from (for example) identify > > Programs return an integer value. Â This is also called the exit > status. Sheer greed, for identify I may get either a return value or an exit status (bad input etc) :-) Looks like subprocess can hack it though. > > What you want is the output of the program. Â For this you need to > capture the output and parse it. > > Look at the subprocess module. Will do. tks D'Arcy (and Benjamin) -- Dave Pawson XSLT XSL-FO FAQ. Docbook FAQ. http://www.dpawson.co.uk
From: Thomas Jollans on 28 Jun 2010 12:26
On 06/28/2010 06:08 PM, Dave Pawson wrote: > Thanks for the replies (and Benjamin). > Not met with the subprocess idea. > > On 28 June 2010 16:29, D'Arcy J.M. Cain <darcy(a)druid.net> wrote: > >>> Main queries are: >>> Ease of calling out to bash to use something like imageMagick or Java? >> >> You don't need to call bash to call an external program. Check out the >> subprocess module. > > Will do. > > If you do need a shell to simplify calling a >> program (environment and wild card expansione.g.) don't call bash. > > I can get what I want from Python. No envars needed. > > > >>> Ease of grabbing return parameters? E.g. convert can return both >>> height and width of an image. Can this be returned to the Python program? >> >> Just to set the terminology straight, a parameter is what you call the >> function with. The return value is what it returns. The program >> output is what it emits (prints.) > > My bad. I mean return values, though I do want > program out from (for example) identify If you're working with images, have a look at the PIL (Python Imaging Library). > > >> >> Programs return an integer value. This is also called the exit >> status. > > Sheer greed, for identify I may get either a return value or an exit > status (bad input etc) :-) > Looks like subprocess can hack it though. > >> >> What you want is the output of the program. For this you need to >> capture the output and parse it. >> >> Look at the subprocess module. > > Will do. > tks D'Arcy (and Benjamin) > > > > > |