Is There A Python Equivalent To The 'which' Command

Put another way, is there a cross-platform way of knowing which file will be executed by subprocess.Popen(file) without first executing it?

Solution 1:

Python 3.3 added shutil.which() to provide a cross-platform means of discovering executables:

http://docs.python.org/3.3/library/shutil.html#shutil.which

Return the path to an executable which would be run if the given cmd was called. If no cmd would be called, return None.

Sample calls:

>>> shutil.which("python")
'/usr/local/bin/python'>>> shutil.which("python")
'C:\\Python33\\python.EXE'

Unfortunately, this has not been backported to 2.7.x.

Solution 2:

An option for Python 2 and 3:

from distutils.spawn import find_executable

find_executable('python')  # '/usr/bin/python'

find_executable('does_not_exist')  # None

find_executable(executable, path=None) simply tries to find 'executable' in the directories listed in 'path'. Defaults to os.environ['PATH'] if 'path' is None. Returns the complete path to 'executable' or None if not found.

Keep in mind that unlike which, find_executable does not actually check that the result is marked as executable. You may want to call os.access(path, os.X_OK) to check that on your own if you want to be certain that subprocess.Popen will be able to execute the file.

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Also of note, shutil.which of Python 3.3+ has been backported and made available for Python 2.6, 2.7, and 3.x via the 3rd-party module whichcraft.

It is available for installation via the aforementioned GitHub page (i.e. pip install git+https://github.com/pydanny/whichcraft.git) or the Python package index (i.e. pip install whichcraft). It can be used like such:

from whichcraft import whichwhich('wget')  # '/usr/bin/wget'

Solution 3:

I believe there is none in the python libraries

>>> def which(pgm):
    path=os.getenv('PATH')
    for p inpath.split(os.path.pathsep):
        p=os.path.join(p,pgm)
        ifos.path.exists(p) andos.access(p,os.X_OK):
            return p


>>> os.which=which
>>> os.which('ls.exe')
'C:\\GNUwin32\\bin\\ls.exe'