def make_dir(dir_name, linux_mode=0o755, error_if_not_writable=False):
    """
    Creates a directory, if it doesn't exist already. If the directory does exist, and <error_if_not_writable> is True,
    the directory will be checked for writability.
    :param str|unicode dir_name: The name of the directory to create
    :param int linux_mode: The mode/permissions to set for the new directory expressed as an octal integer (ex. 0o755)
    :param bool error_if_not_writable: The name of the file to read
    """
    if not os.path.exists(dir_name):
        os.makedirs(dir_name, linux_mode)
    elif error_if_not_writable:
        if not os.access(dir_name, os.R_OK | os.W_OK | os.X_OK):
            raise IOError('Directory {0} is not writable.'.format(dir_name))
Creates a directory, if it doesn't exist already. If the directory does exist, and <error_if_not_writable> is True,
    the directory will be checked for writability.
    :param str|unicode dir_name: The name of the directory to create
    :param int linux_mode: The mode/permissions to set for the new directory expressed as an octal integer (ex. 0o755)
    :param bool error_if_not_writable: The name of the file to read