如何在Python中使用此bash测试构造？

Question

I have a bash snippet I would like to port over to Python. It finds where SVN is located and whether it is executable.

SVN=`which svn 2>&1` 
if [[ ! -x $SVN ]]; then
    echo "A subversion binary could not be found ($SVN)"        
fi

Here is my current attempt in Python using the subprocess module:

SVN = Popen('which svn 2>&1', shell=True, stdout=PIPE).communicate()[0]
Popen("if [[ ! -x SVN ]]; then echo 'svn could not be found or executed'; fi", shell=True)

This does not work because while I do have the location of SVN saved in the local namespace of Python, I can't access it from Popen.

I also tried combining into one Popen object:

Popen("if [[ ! -x 'which svn 2>&1']]; then echo 'svn could not be found'; fi", shell=True)

But I get this error (and needless to say, looks very unwieldy)

/bin/sh: -c: line 0: syntax error near `;'
/bin/sh: -c: line 0: `if [[ ! -x 'which svn 2>&1']]; then echo 'svn could not be found'; fi'

Is there a Python version of the test construct "-x"? I think that would be ideal. Other workarounds would be appreciated as well.

Thanks

Answer 1

This is the simplest solution:

path_to_svn = shutil.which('svn')
is_executable = os.access(path_to_svn, os.X_OK)

shutil.which is new in Python 3.3; there's a polyfill in this answer . You could grab the path from Popen too if you really want, but that's not necessary.

And here are the docs for os.access .

Answer 2

SVN = Popen('which svn 2>&1', shell=True, stdout=PIPE).communicate()[0]
str="if [[ ! -x " + SVN + " ]]; then echo 'svn could not be found or executed'; fi"
Popen(str, shell=True)

Answer 3

There is no need to use which, you can already try to run svn without parameters and if it works it means it's there.

try:
    SVN = subprocess.Popen('svn')
    SVN.wait()
    print "svn exists"
except OSError:
    print "svn does not exist"