def which()

in aws_lambda_builders/utils.py [0:0]

• 34 lines of code
• 7 McCabe index (conditional complexity)

def which(cmd, mode=os.F_OK | os.X_OK, executable_search_paths=None):  # pragma: no cover
    """Given a command, mode, and executable search paths list, return the paths which
    conforms to the given mode on the PATH with the prepended additional search paths,
    or None if there is no such file.
    `mode` defaults to os.F_OK | os.X_OK. the default search `path` defaults
    to the result of os.environ.get("PATH")
    Note: This function was backported from the Python 3 source code.

    :type cmd: str
    :param cmd:
        Executable to be looked up in PATH.

    :type mode: str
    :param mode:
        Modes of access for the executable.

    :type executable_search_paths: list
    :param executable_search_paths:
        List of paths to look for `cmd` in preference order.
    """

    # 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

    path = os.environ.get("PATH", os.defpath)

    if not path:
        return None

    path = path.split(os.pathsep)

    if executable_search_paths:
        path = executable_search_paths + path

    if sys.platform == "win32":
        # The current directory takes precedence on Windows.
        if os.curdir not 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()
    paths = []

    for dir in path:
        normdir = os.path.normcase(dir)
        if normdir not in seen:
            seen.add(normdir)
            for thefile in files:
                name = os.path.join(dir, thefile)
                if _access_check(name, mode):
                    paths.append(name)
    return paths