[Tutor] Python working with Bash....arrrggggh!

[eryksun]

On Thu, Aug 23, 2012 at 11:55 PM, Ray Jones <crawlzone at gmail.com> wrote:

> For example, if I wish to test if a file exists, I might do
>
> test = Popen('[ -f file-i-want-to-test-for ]')
>
> But the moment I invoke Bash for a test, I must deal with the fact that
> Bash returns a zero for true and a non-zero for false. But in Python,

Please see os.path:

http://docs.python.org/library/os.path

That said, you can use check_call and check_output if you want a more
Pythonic interface. These raise an exception for a non-zero return
code. For example:

# check.py

from subprocess import check_call, CalledProcessError

try:

    # in Debian [ is at /usr/bin/[
    rc = check_call(["/usr/bin/[", "-f", "check.py", "]"])
    print "success:", rc

    # or pass the command string to the shell
    rc = check_call("[ -f check.py ]", shell=True)
    print "success:", rc

    # force a failure
    rc = check_call("[ -f notfound ]", shell=True)
    print "success:", rc  # this won't execute

except CalledProcessError as e:
    print "failed: %d" % e.returncode