'Return True if a symbolic link or file exists and is executable, but if full_path
is a directory, return False.'

def assert_file_executable(self, full_path):

    if (full_path is None):
        return False
    if os.path.isdir(full_path):
        return False
    if os.path.exists(full_path):
        if ((stat.S_IXUSR & os.stat(full_path)[stat.ST_MODE]) == 64):
            return True
    return False
