Test if executable exists in Python

Question

In Python  is there a portable and simple way to test if an executable program exists   By simple I mean something like the which command which would be just perfect  I don t want to search PATH manually or something involving trying to execute it with Popen  amp  al and see if it fails  that s what I m doing now  but imagine it s launchmissiles

User · Answer

Just remember to specify the file extension on windows. Otherwise, you have to write a much complicated is_exe for windows using PATHEXT environment variable. You may just want to use FindPath.

OTOH, why are you even bothering to search for the executable? The operating system will do it for you as part of popen call & will raise an exception if the executable is not found. All you need to do is catch the correct exception for given OS. Note that on Windows, subprocess.Popen(exe, shell=True) will fail silently if exe is not found.

Incorporating PATHEXT into the above implementation of which (in Jay's answer):

def which(program):
    def is_exe(fpath):
        return os.path.exists(fpath) and os.access(fpath, os.X_OK) and os.path.isfile(fpath)

    def ext_candidates(fpath):
        yield fpath
        for ext in os.environ.get("PATHEXT", "").split(os.pathsep):
            yield fpath + ext

    fpath, fname = os.path.split(program)
    if fpath:
        if is_exe(program):
            return program
    else:
        for path in os.environ["PATH"].split(os.pathsep):
            exe_file = os.path.join(path, program)
            for candidate in ext_candidates(exe_file):
                if is_exe(candidate):
                    return candidate

    return None

User · Answer

Easiest way I can think of    def which program       import os     def is exe fpath           return os path isfile fpath  and os access fpath  os X OK       fpath  fname   os path split program      if fpath          if is exe program               return program     else          for path in os environ  PATH   split os pathsep               exe file   os path join path  program              if is exe exe file                   return exe file      return None   Edit  Updated code sample to include logic for handling case where provided argument is already a full path to the executable  i e   which  bin ls   This mimics the behavior of the UNIX  which  command   Edit  Updated to use os path isfile   instead of os path exists   per comments   Edit  path strip      seems like the wrong thing to do here  Neither Windows nor POSIX appear to encourage quoted PATH items

User · Answer

This seems simple enough and works both in python 2 and 3  try  subprocess check output  which executable  shell True  except  sys exit  ERROR  executable not found

User · Answer

For python 3 3 and later  import shutil  command    ls  shutil which command  is not None  As a one-liner of Jan-Philip Gehrcke Answer  cmd exists   lambda x  shutil which x  is not None  As a def  def cmd exists cmd       return shutil which cmd  is not None   For python 3 2 and earlier  my command    ls  any                os access os path join path  my command   os X OK           and os path isfile os path join path  my command            for path in os environ  quot PATH quot   split os pathsep     This is a one-liner of Jay s Answer  Also here as a lambda func  cmd exists   lambda x  any  os access os path join path  x   os X OK  and os path isfile os path join path  x    for path in os environ  quot PATH quot   split os pathsep   cmd exists  ls    Or lastly  indented as a function  def cmd exists cmd  path None        quot  quot  quot  test if path contains an executable file with name      quot  quot  quot      if path is None          path   os environ  quot PATH quot   split os pathsep       for prefix in path          filename   os path join prefix  cmd          executable   os access filename  os X OK          is not directory   os path isfile filename          if executable and is not directory              return True     return False

User · Answer

You can try the external lib called  sh   http   amoffat github io sh     import sh print sh which  ls      prints   bin ls  depending on your setup print sh which  xxx     prints None

User · Answer

Easiest way I can think of    def which program       import os     def is exe fpath           return os path isfile fpath  and os access fpath  os X OK       fpath  fname   os path split program      if fpath          if is exe program               return program     else          for path in os environ  PATH   split os pathsep               exe file   os path join path  program              if is exe exe file                   return exe file      return None   Edit  Updated code sample to include logic for handling case where provided argument is already a full path to the executable  i e   which  bin ls   This mimics the behavior of the UNIX  which  command   Edit  Updated to use os path isfile   instead of os path exists   per comments   Edit  path strip      seems like the wrong thing to do here  Neither Windows nor POSIX appear to encourage quoted PATH items

User · Answer

Use shutil which   from Python s wonderful standard library  Batteries included

User · Answer

See os path module for some useful functions on pathnames  To check if an existing file is executable  use os access path  mode   with the os X OK mode   os X OK Value to include in the mode parameter of access   to determine if path can be executed   EDIT  The suggested which   implementations are missing one clue - using os path join   to build full file names

User · Answer

Easiest way I can think of    def which program       import os     def is exe fpath           return os path isfile fpath  and os access fpath  os X OK       fpath  fname   os path split program      if fpath          if is exe program               return program     else          for path in os environ  PATH   split os pathsep               exe file   os path join path  program              if is exe exe file                   return exe file      return None   Edit  Updated code sample to include logic for handling case where provided argument is already a full path to the executable  i e   which  bin ls   This mimics the behavior of the UNIX  which  command   Edit  Updated to use os path isfile   instead of os path exists   per comments   Edit  path strip      seems like the wrong thing to do here  Neither Windows nor POSIX appear to encourage quoted PATH items

User · Answer

So basically you want to find a file in mounted filesystem  not necessarily in PATH directories only  and check if it is executable  This translates to following plan     enumerate all files in locally mounted filesystems match results with name pattern for each file found check if it is executable   I d say  doing this in a portable way will require lots of computing power and time  Is it really what you need

User · Answer

Just remember to specify the file extension on windows. Otherwise, you have to write a much complicated is_exe for windows using PATHEXT environment variable. You may just want to use FindPath.

OTOH, why are you even bothering to search for the executable? The operating system will do it for you as part of popen call & will raise an exception if the executable is not found. All you need to do is catch the correct exception for given OS. Note that on Windows, subprocess.Popen(exe, shell=True) will fail silently if exe is not found.

Incorporating PATHEXT into the above implementation of which (in Jay's answer):

def which(program):
    def is_exe(fpath):
        return os.path.exists(fpath) and os.access(fpath, os.X_OK) and os.path.isfile(fpath)

    def ext_candidates(fpath):
        yield fpath
        for ext in os.environ.get("PATHEXT", "").split(os.pathsep):
            yield fpath + ext

    fpath, fname = os.path.split(program)
    if fpath:
        if is_exe(program):
            return program
    else:
        for path in os.environ["PATH"].split(os.pathsep):
            exe_file = os.path.join(path, program)
            for candidate in ext_candidates(exe_file):
                if is_exe(candidate):
                    return candidate

    return None

User · Answer

Added windows support  def which program       path ext             ext list   None      if sys platform     win32           ext list    ext lower   for ext in os environ  PATHEXT   split            def is exe fpath           exe   os path isfile fpath  and os access fpath  os X OK            search for executable under windows         if not exe              if ext list                  for ext in ext list                      exe path     s s     fpath ext                      if os path isfile exe path  and os access exe path  os X OK                           path ext 0    ext                         return True                 return False         return exe      fpath  fname   os path split program       if fpath          if is exe program               return   s s     program  path ext 0       else          for path in os environ  PATH   split os pathsep               path   path strip                  exe file   os path join path  program              if is exe exe file                   return   s s     exe file  path ext 0       return None

User · Answer

An important question is  Why do you need to test if executable exist   Maybe you don t   -    Recently I needed this functionality to launch viewer for PNG file  I wanted to iterate over some predefined viewers and run the first that exists  Fortunately  I came across os startfile  It s much better  Simple  portable and uses the default viewer on the system    gt  gt  gt  os startfile  yourfile png     Update  I was wrong about os startfile being portable    It s Windows only  On Mac you have to run open command  And xdg open on Unix  There s a Python issue on adding Mac and Unix support for os startfile

User · Answer

Added windows support  def which program       path ext             ext list   None      if sys platform     win32           ext list    ext lower   for ext in os environ  PATHEXT   split            def is exe fpath           exe   os path isfile fpath  and os access fpath  os X OK            search for executable under windows         if not exe              if ext list                  for ext in ext list                      exe path     s s     fpath ext                      if os path isfile exe path  and os access exe path  os X OK                           path ext 0    ext                         return True                 return False         return exe      fpath  fname   os path split program       if fpath          if is exe program               return   s s     program  path ext 0       else          for path in os environ  PATH   split os pathsep               path   path strip                  exe file   os path join path  program              if is exe exe file                   return   s s     exe file  path ext 0       return None

User · Answer

See os path module for some useful functions on pathnames  To check if an existing file is executable  use os access path  mode   with the os X OK mode   os X OK Value to include in the mode parameter of access   to determine if path can be executed   EDIT  The suggested which   implementations are missing one clue - using os path join   to build full file names

User · Answer

This seems simple enough and works both in python 2 and 3  try  subprocess check output  which executable  shell True  except  sys exit  ERROR  executable not found

User · Answer

So basically you want to find a file in mounted filesystem  not necessarily in PATH directories only  and check if it is executable  This translates to following plan     enumerate all files in locally mounted filesystems match results with name pattern for each file found check if it is executable   I d say  doing this in a portable way will require lots of computing power and time  Is it really what you need

User · Answer

So basically you want to find a file in mounted filesystem  not necessarily in PATH directories only  and check if it is executable  This translates to following plan     enumerate all files in locally mounted filesystems match results with name pattern for each file found check if it is executable   I d say  doing this in a portable way will require lots of computing power and time  Is it really what you need

User · Answer

Just remember to specify the file extension on windows. Otherwise, you have to write a much complicated is_exe for windows using PATHEXT environment variable. You may just want to use FindPath.

OTOH, why are you even bothering to search for the executable? The operating system will do it for you as part of popen call & will raise an exception if the executable is not found. All you need to do is catch the correct exception for given OS. Note that on Windows, subprocess.Popen(exe, shell=True) will fail silently if exe is not found.

Incorporating PATHEXT into the above implementation of which (in Jay's answer):

def which(program):
    def is_exe(fpath):
        return os.path.exists(fpath) and os.access(fpath, os.X_OK) and os.path.isfile(fpath)

    def ext_candidates(fpath):
        yield fpath
        for ext in os.environ.get("PATHEXT", "").split(os.pathsep):
            yield fpath + ext

    fpath, fname = os.path.split(program)
    if fpath:
        if is_exe(program):
            return program
    else:
        for path in os.environ["PATH"].split(os.pathsep):
            exe_file = os.path.join(path, program)
            for candidate in ext_candidates(exe_file):
                if is_exe(candidate):
                    return candidate

    return None

User · Answer

See os path module for some useful functions on pathnames  To check if an existing file is executable  use os access path  mode   with the os X OK mode   os X OK Value to include in the mode parameter of access   to determine if path can be executed   EDIT  The suggested which   implementations are missing one clue - using os path join   to build full file names

User · Answer

There is a which py script in a standard Python distribution  e g  on Windows   PythonXX Tools Scripts which py      EDIT  which py depends on ls therefore it is not cross-platform

User · Answer

For  nix platforms  Linux and OS X   This seems to be working for me   Edited to work on Linux  thanks to Mestreion  def cmd exists cmd       return subprocess call  type     cmd  shell True           stdout subprocess PIPE  stderr subprocess PIPE     0   What we re doing here is using the builtin command type and checking the exit code  If there s no such command  type will exit with 1  or a non-zero status code anyway    The bit about stdout and stderr is just to silence the output of the type command  since we re only interested in the exit status code   Example usage    gt  gt  gt  cmd exists  jsmin   True  gt  gt  gt  cmd exists  cssmin   False  gt  gt  gt  cmd exists  ls   True  gt  gt  gt  cmd exists  dir   False  gt  gt  gt  cmd exists  node   True  gt  gt  gt  cmd exists  steam   False

User · Answer

So basically you want to find a file in mounted filesystem  not necessarily in PATH directories only  and check if it is executable  This translates to following plan     enumerate all files in locally mounted filesystems match results with name pattern for each file found check if it is executable   I d say  doing this in a portable way will require lots of computing power and time  Is it really what you need

User · Answer

I know that I m being a bit of a necromancer here  but I stumbled across this question and the accepted solution didn t work for me for all cases Thought it might be useful to submit anyway  In particular  the  executable  mode detection  and the requirement of supplying the file extension  Furthermore  both python3 3 s shutil which  uses PATHEXT  and python2 4  s distutils spawn find executable  just tries adding   exe   only work in a subset of cases   So I wrote a  super  version  based on the accepted answer  and the PATHEXT suggestion from Suraj   This version of which does the task a bit more thoroughly  and tries a series of  broadphase  breadth-first techniques first  and eventually tries more fine-grained searches over the PATH space   import os import sys import stat import tempfile   def is case sensitive filesystem        tmphandle  tmppath   tempfile mkstemp       is insensitive   os path exists tmppath upper        os close tmphandle      os remove tmppath      return not is insensitive   IS CASE SENSITIVE FILESYSTEM   is case sensitive filesystem     def which program  case sensitive  IS CASE SENSITIVE FILESYSTEM           Simulates unix  which  command  Returns absolute path if program found         def is exe fpath               Return true if fpath is a file we have access to that is executable             accessmode   os F OK   os X OK         if os path exists fpath  and os access fpath  accessmode  and not os path isdir fpath               filemode   os stat fpath  st mode             ret   bool filemode  amp  stat S IXUSR or filemode  amp  stat S IXGRP or filemode  amp  stat S IXOTH              return ret      def list file exts directory  search filename None  ignore case True               Return list of  filename  extension  tuples which match the search filename            if ignore case              search filename   search filename lower           for root  dirs  files in os walk path               for f in files                  filename  extension   os path splitext f                  if ignore case                      filename   filename lower                   if not search filename or filename    search filename                      yield  filename  extension              break      fpath  fname   os path split program         is a path  try direct program path     if fpath          if is exe program               return program     elif  win  in sys platform            isnt a path  try fname in current directory on windows         if is exe fname               return program      paths    path strip      for path in os environ get  PATH       split os pathsep       exe exts    ext for ext in os environ get  PATHEXT       split os pathsep       if not case sensitive          exe exts   map str lower  exe exts         try append program path per directory     for path in paths          exe file   os path join path  program          if is exe exe file               return exe file        try with known executable extensions per program path per directory     for path in paths          filepath   os path join path  program          for extension in exe exts              exe file   filepath extension             if is exe exe file                   return exe file        try search program name with  soft  extension search     if len os path splitext fname  1      0          for path in paths              file exts   list file exts path  fname  not case sensitive              for file ext in file exts                  filename      join file ext                  exe file   os path join path  filename                  if is exe exe file                       return exe file      return None   Usage looks like this    gt  gt  gt  which which  meld    C   Program Files  x86   Meld  meld  meld exe    The accepted solution did not work for me in this case  since there were files like meld 1  meld ico  meld doap  etc also in the directory  one of which were returned instead  presumably since lexicographically first  because the executable test in the accepted answer was incomplete and giving false positives

User · Answer

There is a which py script in a standard Python distribution  e g  on Windows   PythonXX Tools Scripts which py      EDIT  which py depends on ls therefore it is not cross-platform

User · Answer

An important question is  Why do you need to test if executable exist   Maybe you don t   -    Recently I needed this functionality to launch viewer for PNG file  I wanted to iterate over some predefined viewers and run the first that exists  Fortunately  I came across os startfile  It s much better  Simple  portable and uses the default viewer on the system    gt  gt  gt  os startfile  yourfile png     Update  I was wrong about os startfile being portable    It s Windows only  On Mac you have to run open command  And xdg open on Unix  There s a Python issue on adding Mac and Unix support for os startfile

User · Answer

I know this is an ancient question  but you can use distutils spawn find executable   This has  been documented since python 2 4 and has existed since python 1 6   import distutils spawn distutils spawn find executable  notepad exe     Also  Python 3 3 now offers shutil which

User · Answer

On the basis that it is easier to ask forgiveness than permission  and  importantly  that the command is safe to run  I would just try to use it and catch the error  OSError in this case - I checked for file does not exist and file is not executable and they both give OSError   It helps if the executable has something like a --version flag that is a quick no-op  import subprocess myexec    quot python2 8 quot  try      subprocess call  myexec   --version   except OSError      print  quot  s not found on path quot    myexec  This is not a general solution  but will be the easiest way for a lot of use cases - those where the code needs to look for a single well known executable which is safe to run  or at least safe to run with a given flag

User · Answer

I know that I m being a bit of a necromancer here  but I stumbled across this question and the accepted solution didn t work for me for all cases Thought it might be useful to submit anyway  In particular  the  executable  mode detection  and the requirement of supplying the file extension  Furthermore  both python3 3 s shutil which  uses PATHEXT  and python2 4  s distutils spawn find executable  just tries adding   exe   only work in a subset of cases   So I wrote a  super  version  based on the accepted answer  and the PATHEXT suggestion from Suraj   This version of which does the task a bit more thoroughly  and tries a series of  broadphase  breadth-first techniques first  and eventually tries more fine-grained searches over the PATH space   import os import sys import stat import tempfile   def is case sensitive filesystem        tmphandle  tmppath   tempfile mkstemp       is insensitive   os path exists tmppath upper        os close tmphandle      os remove tmppath      return not is insensitive   IS CASE SENSITIVE FILESYSTEM   is case sensitive filesystem     def which program  case sensitive  IS CASE SENSITIVE FILESYSTEM           Simulates unix  which  command  Returns absolute path if program found         def is exe fpath               Return true if fpath is a file we have access to that is executable             accessmode   os F OK   os X OK         if os path exists fpath  and os access fpath  accessmode  and not os path isdir fpath               filemode   os stat fpath  st mode             ret   bool filemode  amp  stat S IXUSR or filemode  amp  stat S IXGRP or filemode  amp  stat S IXOTH              return ret      def list file exts directory  search filename None  ignore case True               Return list of  filename  extension  tuples which match the search filename            if ignore case              search filename   search filename lower           for root  dirs  files in os walk path               for f in files                  filename  extension   os path splitext f                  if ignore case                      filename   filename lower                   if not search filename or filename    search filename                      yield  filename  extension              break      fpath  fname   os path split program         is a path  try direct program path     if fpath          if is exe program               return program     elif  win  in sys platform            isnt a path  try fname in current directory on windows         if is exe fname               return program      paths    path strip      for path in os environ get  PATH       split os pathsep       exe exts    ext for ext in os environ get  PATHEXT       split os pathsep       if not case sensitive          exe exts   map str lower  exe exts         try append program path per directory     for path in paths          exe file   os path join path  program          if is exe exe file               return exe file        try with known executable extensions per program path per directory     for path in paths          filepath   os path join path  program          for extension in exe exts              exe file   filepath extension             if is exe exe file                   return exe file        try search program name with  soft  extension search     if len os path splitext fname  1      0          for path in paths              file exts   list file exts path  fname  not case sensitive              for file ext in file exts                  filename      join file ext                  exe file   os path join path  filename                  if is exe exe file                       return exe file      return None   Usage looks like this    gt  gt  gt  which which  meld    C   Program Files  x86   Meld  meld  meld exe    The accepted solution did not work for me in this case  since there were files like meld 1  meld ico  meld doap  etc also in the directory  one of which were returned instead  presumably since lexicographically first  because the executable test in the accepted answer was incomplete and giving false positives

User · Answer

Just remember to specify the file extension on windows. Otherwise, you have to write a much complicated is_exe for windows using PATHEXT environment variable. You may just want to use FindPath.

OTOH, why are you even bothering to search for the executable? The operating system will do it for you as part of popen call & will raise an exception if the executable is not found. All you need to do is catch the correct exception for given OS. Note that on Windows, subprocess.Popen(exe, shell=True) will fail silently if exe is not found.

Incorporating PATHEXT into the above implementation of which (in Jay's answer):

def which(program):
    def is_exe(fpath):
        return os.path.exists(fpath) and os.access(fpath, os.X_OK) and os.path.isfile(fpath)

    def ext_candidates(fpath):
        yield fpath
        for ext in os.environ.get("PATHEXT", "").split(os.pathsep):
            yield fpath + ext

    fpath, fname = os.path.split(program)
    if fpath:
        if is_exe(program):
            return program
    else:
        for path in os.environ["PATH"].split(os.pathsep):
            exe_file = os.path.join(path, program)
            for candidate in ext_candidates(exe_file):
                if is_exe(candidate):
                    return candidate

    return None

User · Answer

I know this is an ancient question  but you can use distutils spawn find executable   This has  been documented since python 2 4 and has existed since python 1 6   import distutils spawn distutils spawn find executable  notepad exe     Also  Python 3 3 now offers shutil which

User · Answer

Easiest way I can think of    def which program       import os     def is exe fpath           return os path isfile fpath  and os access fpath  os X OK       fpath  fname   os path split program      if fpath          if is exe program               return program     else          for path in os environ  PATH   split os pathsep               exe file   os path join path  program              if is exe exe file                   return exe file      return None   Edit  Updated code sample to include logic for handling case where provided argument is already a full path to the executable  i e   which  bin ls   This mimics the behavior of the UNIX  which  command   Edit  Updated to use os path isfile   instead of os path exists   per comments   Edit  path strip      seems like the wrong thing to do here  Neither Windows nor POSIX appear to encourage quoted PATH items

User · Answer

On the basis that it is easier to ask forgiveness than permission  and  importantly  that the command is safe to run  I would just try to use it and catch the error  OSError in this case - I checked for file does not exist and file is not executable and they both give OSError   It helps if the executable has something like a --version flag that is a quick no-op  import subprocess myexec    quot python2 8 quot  try      subprocess call  myexec   --version   except OSError      print  quot  s not found on path quot    myexec  This is not a general solution  but will be the easiest way for a lot of use cases - those where the code needs to look for a single well known executable which is safe to run  or at least safe to run with a given flag

User · Answer

There is a which py script in a standard Python distribution  e g  on Windows   PythonXX Tools Scripts which py      EDIT  which py depends on ls therefore it is not cross-platform

User · Answer

For  nix platforms  Linux and OS X   This seems to be working for me   Edited to work on Linux  thanks to Mestreion  def cmd exists cmd       return subprocess call  type     cmd  shell True           stdout subprocess PIPE  stderr subprocess PIPE     0   What we re doing here is using the builtin command type and checking the exit code  If there s no such command  type will exit with 1  or a non-zero status code anyway    The bit about stdout and stderr is just to silence the output of the type command  since we re only interested in the exit status code   Example usage    gt  gt  gt  cmd exists  jsmin   True  gt  gt  gt  cmd exists  cssmin   False  gt  gt  gt  cmd exists  ls   True  gt  gt  gt  cmd exists  dir   False  gt  gt  gt  cmd exists  node   True  gt  gt  gt  cmd exists  steam   False

User · Answer

You can try the external lib called  sh   http   amoffat github io sh     import sh print sh which  ls      prints   bin ls  depending on your setup print sh which  xxx     prints None

User · Answer

For python 3 3 and later  import shutil  command    ls  shutil which command  is not None  As a one-liner of Jan-Philip Gehrcke Answer  cmd exists   lambda x  shutil which x  is not None  As a def  def cmd exists cmd       return shutil which cmd  is not None   For python 3 2 and earlier  my command    ls  any                os access os path join path  my command   os X OK           and os path isfile os path join path  my command            for path in os environ  quot PATH quot   split os pathsep     This is a one-liner of Jay s Answer  Also here as a lambda func  cmd exists   lambda x  any  os access os path join path  x   os X OK  and os path isfile os path join path  x    for path in os environ  quot PATH quot   split os pathsep   cmd exists  ls    Or lastly  indented as a function  def cmd exists cmd  path None        quot  quot  quot  test if path contains an executable file with name      quot  quot  quot      if path is None          path   os environ  quot PATH quot   split os pathsep       for prefix in path          filename   os path join prefix  cmd          executable   os access filename  os X OK          is not directory   os path isfile filename          if executable and is not directory              return True     return False

User · Answer

See os path module for some useful functions on pathnames  To check if an existing file is executable  use os access path  mode   with the os X OK mode   os X OK Value to include in the mode parameter of access   to determine if path can be executed   EDIT  The suggested which   implementations are missing one clue - using os path join   to build full file names

User · Answer

Use shutil which   from Python s wonderful standard library  Batteries included

User · Answer

There is a which py script in a standard Python distribution  e g  on Windows   PythonXX Tools Scripts which py      EDIT  which py depends on ls therefore it is not cross-platform

[python] Test if executable exists in Python?

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