Using ruby gem/command from python

Question

I've installed the Ruby gem 'haml' on my mac, which I can use to compile haml files into html files using the following command at the terminal:

haml 'path/to/haml/file.haml' 'desired/html/path/file.html'

This command simply creates an html file at the second path, and gives no output in the terminal. So for example, this command:

haml "/Volumes/Macintosh HD/Users/me/Sites/ICSP/sugar.haml" "/Volumes/Macintosh HD/Users/me/Sites/ICSP/sugar.html"

Creates a sugar.html file at the given path. Now I'm trying to use this functionality from a python script. When I type this into IDLE's interactive python shell:

>>>import subprocess
>>>subprocess.Popen('haml "/Volumes/Macintosh HD/Users/me/Sites/ICSP/sugar.haml"        "/Volumes/Macintosh HD/Users/me/Sites/ICSP/sugar.html"', shell=True, executable='/bin/bash')
<subprocess.Popen object at 0x159d6f0>

I get output suggesting that the process has been run, however, there is no file outputted. Why is this happening? I even put in the Shell argument, but no interactive shell shows up. Also, I read somewhere that the default shell used is not bash, which is what the Mac terminal uses, so I put that in too for good measure.

Following icktoofay's advice, I ran check_call. Here is the traceback I received:

Traceback (most recent call last):
File "/Users/neil/Desktop/subprocesstest.py", line 7, in p = subprocess.check_call(x, shell=True) File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/subprocess.py", line 504, in check_call raise CalledProcessError(retcode, cmd) CalledProcessError: Command 'haml "/Volumes/Macintosh HD/Users/neil/Sites/ICSP/sugar.haml" "/Volumes/Macintosh HD/Users/neil/Sites/ICSP/sugar.html"' returned non-zero exit status 127

According to the bash reference manual, while searching for a command to be executed,

If the name is neither a shell function nor a builtin, and contains no slashes, Bash searches each element of $PATH for a directory containing an executable file by that name. ... If that function is not defined, the shell prints an error message and returns an exit status of 127.

However, I thought it was indeed finding the haml command after adding the shell and executable arguments, because before that, it was giving a 'file or directory not found error', which indicates that the function is not executable directly but rather in a shell only.

Now how do I make python find this haml command? Or would I have to use some ugly workaround like an applescript which then invokes the haml command.

Have you tried using subprocess.check_call instead of directly using subprocess.Popen? — icktoofay
– icktoofay, Commented Jun 4, 2011 at 20:37
Sorry the question seems so long now, but I've tried to provide as much information as possible to make debugging easier. — Neil
– Neil, Commented Jun 4, 2011 at 20:59
You've probably tried something like this, but does this work (with the paths changed obviously)? subprocess.check_call(['/path/to/haml', '/your/file.haml', '/your/file.html']) — icktoofay
– icktoofay, Commented Jun 4, 2011 at 21:03
Turns out putting the full path to haml in the original call works perfectly. Now how do I make this device independent, ie, how can I make python find haml? Or should I ask users of the script to put haml into their system path or something? — Neil
– Neil, Commented Jun 6, 2011 at 10:43

Zach Kelling · Accepted Answer · 2011-06-05 18:30:14Z

2

I see that you are using, shell=True, so I would have expected things to just work. Checked it locally here with Python 2.7.1 and haml 3.1.1 and I had no problems executing it. There are also some python implementations you might be interested in, PyHAML, HamlPy, djaml or django-haml.

import subprocess
subprocess.Popen(['haml', 'hello.haml', 'hello.html'], shell=True)

% cat hello.html
<strong class='code' id='message'>Hello, World!</strong>

edited Jun 5, 2011 at 18:30

answered Jun 4, 2011 at 21:18

Zach Kelling

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2 Comments

Neil Over a year ago

I did actually use the shell=True argument. I'll try using the full path to haml, but since I'm guessing this would vary from computer to computer, it would be difficult to turn this into a distributable script. Also, I did look up the python implementations earlier, but it seems like they're not just a python bridge to call the haml compiler, they actually handle the compiling themselves, sometimes resulting in a different output than the official haml gem's output. I'd rather not risk using a python implementation that might fall behind in syntax support in the future.

Zach Kelling Over a year ago

@Neil ah I see that now. Should just work then. Very odd. Maybe a bug with haml? I just tested it and it works fine for me.

Pavel Repin · Accepted Answer · 2011-06-05 03:20:54Z

0

shlex.split() is your friend, when you want to build args list suitable for Popen and its ilk.

>>> import subprocess
>>> import shlex
>>> p = subprocess.Popen(shlex.split('haml "/Volumes/Macintosh HD/Users/me/Sites/ICSP/sugar.haml" "/Volumes/Macintosh HD/Users/me/Sites/ICSP/sugar.html"'))
>>> p.wait()
0

answered Jun 5, 2011 at 3:20

Pavel Repin

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