Is there a Python equivalent to the 'which' command

Question

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

By default, subprocess inherents the environment of the parent process. So for any executable in the PATH (or the OS in question's equivalent) you don't need to specifiy the location. — Roland Smith, Mar 26 '12 at 20:12

score 85 · Answer 1 · answered Jun 10 '13 at 13:39

85

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.

answered Jun 10 '13 at 13:39

joemaller

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Python source for version 3.3's implementation of shutil.which is here (only a few dozen lines): http://hg.python.org/cpython/file/6860263c05b3/Lib/shutil.py#l1068 – joemaller Jun 10 '13 at 13:53
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if you change line 1110 to `if any([cmd.lower().endswith(ext.lower()) for ext in pathext])` (turn the generator to a list) than it will work in python 2.7. – Chris Hagmann Apr 11 '14 at 13:01
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Backport available here: https://github.com/mbr/shutilwhich – nu everest Feb 13 '16 at 15:20
shutil.which is also dog slow – Travis Bear Nov 14 '18 at 19:28
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In 2021 this should be the accepted answer. – cjauvin Jan 12 '21 at 23:07

Six · Answer 2 · 2017-05-15T23:37:04.527

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.

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'

Avoid distutils because it used deprecated imp which creates a runtime warning. — sorin, May 03 '20 at 10:15

score 10 · Accepted Answer · edited Apr 01 '22 at 09:25

10

outdated (not longer true)

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'

edited Apr 01 '22 at 09:25

sorin

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answered Mar 26 '12 at 18:45

Abhijit

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Is there a Python equivalent to the 'which' command

3 Answers3

outdated (not longer true)

Linked