parameters: (cmd, mode=os.F_OK | os.X_OK, path=None)
return_statement: return None
docstring: Given a command, mode, and a PATH string, return the path which
      conforms to the given mode on the PATH, or None if there is no such
      file.
  
      `mode` defaults to os.F_OK | os.X_OK. `path` defaults to the result
      of os.environ.get("PATH"), or can be overridden with a custom search
      path.
docstring_summary: Given a command, mode, and a PATH string, return the path which
      conforms to the given mode on the PATH, or None if there is no such
      file.
docstring_tokens: Given a command mode and a PATH string return the path which conforms to the given mode on the PATH or None if there is no such file .
function: def which(cmd, mode=os.F_OK | os.X_OK, path=None):
      """Given a command, mode, and a PATH string, return the path which
      conforms to the given mode on the PATH, or None if there is no such
      file.
  
      `mode` defaults to os.F_OK | os.X_OK. `path` defaults to the result
      of os.environ.get("PATH"), or can be overridden with a custom search
      path.
  
      """
      # Check that a given file can be accessed with the correct mode.
      # Additionally check that `file` is not a directory, as on Windows
      # directories pass the os.access check.
      def _access_check(fn, mode):
          return (os.path.exists(fn) and os.access(fn, mode)
                  and not os.path.isdir(fn))
  
      # If we're given a path with a directory part, look it up directly rather
      # than referring to PATH directories. This includes checking relative to the
      # current directory, e.g. ./script
      if os.path.dirname(cmd):
          if _access_check(cmd, mode):
              return cmd
          return None
  
      if path is None:
          path = os.environ.get("PATH", None)
          if path is None:
              try:
                  path = os.confstr("CS_PATH")
              except (AttributeError, ValueError):
                  # os.confstr() or CS_PATH is not available
                  path = os.defpath
          # bpo-35755: Don't use os.defpath if the PATH environment variable is
          # set to an empty string
  
      # PATH='' doesn't match, whereas PATH=':' looks in the current directory
      if not path:
          return None
      path = path.split(os.pathsep)
  
      if sys.platform == "win32":
          # The current directory takes precedence on Windows.
          if not os.curdir in path:
              path.insert(0, os.curdir)
  
          # PATHEXT is necessary to check on Windows.
          pathext = os.environ.get("PATHEXT", "").split(os.pathsep)
          # See if the given file matches any of the expected path extensions.
          # This will allow us to short circuit when given "python.exe".
          # If it does match, only test that one, otherwise we have to try
          # others.
          if any(cmd.lower().endswith(ext.lower()) for ext in pathext):
              files = [cmd]
          else:
              files = [cmd + ext for ext in pathext]
      else:
          # On other platforms you don't have things like PATHEXT to tell you
          # what file suffixes are executable, so just pass on cmd as-is.
          files = [cmd]
  
      seen = set()
      for dir in path:
          normdir = os.path.normcase(dir)
          if not normdir in seen:
              seen.add(normdir)
              for thefile in files:
                  name = os.path.join(dir, thefile)
                  if _access_check(name, mode):
                      return name
      return None
function_tokens: def which ( cmd , mode = os . F_OK | os . X_OK , path = None ) : # Check that a given file can be accessed with the correct mode. # Additionally check that `file` is not a directory, as on Windows # directories pass the os.access check. def _access_check ( fn , mode ) : return ( os . path . exists ( fn ) and os . access ( fn , mode ) and not os . path . isdir ( fn ) ) # If we're given a path with a directory part, look it up directly rather # than referring to PATH directories. This includes checking relative to the # current directory, e.g. ./script if os . path . dirname ( cmd ) : if _access_check ( cmd , mode ) : return cmd return None if path is None : path = os . environ . get ( "PATH" , None ) if path is None : try : path = os . confstr ( "CS_PATH" ) except ( AttributeError , ValueError ) : # os.confstr() or CS_PATH is not available path = os . defpath # bpo-35755: Don't use os.defpath if the PATH environment variable is # set to an empty string # PATH='' doesn't match, whereas PATH=':' looks in the current directory if not path : return None path = path . split ( os . pathsep ) if sys . platform == "win32" : # The current directory takes precedence on Windows. if not os . curdir in path : path . insert ( 0 , os . curdir ) # PATHEXT is necessary to check on Windows. pathext = os . environ . get ( "PATHEXT" , "" ) . split ( os . pathsep ) # See if the given file matches any of the expected path extensions. # This will allow us to short circuit when given "python.exe". # If it does match, only test that one, otherwise we have to try # others. if any ( cmd . lower ( ) . endswith ( ext . lower ( ) ) for ext in pathext ) : files = [ cmd ] else : files = [ cmd + ext for ext in pathext ] else : # On other platforms you don't have things like PATHEXT to tell you # what file suffixes are executable, so just pass on cmd as-is. files = [ cmd ] seen = set ( ) for dir in path : normdir = os . path . normcase ( dir ) if not normdir in seen : seen . add ( normdir ) for thefile in files : name = os . path . join ( dir , thefile ) if _access_check ( name , mode ) : return name return None