shell – Is there a Python equivalent to the which command

shell – Is there a Python equivalent to the which command

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.

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 which

which(wget)  # /usr/bin/wget

shell – Is there a Python equivalent to the which command

I believe there is none in the python libraries

>>> def which(pgm):
    path=os.getenv(PATH)
    for p in path.split(os.path.pathsep):
        p=os.path.join(p,pgm)
        if os.path.exists(p) and os.access(p,os.X_OK):
            return p


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