Convert a list of canonical DOIs to a list of DOIs URLs.

    :param dois: List of canonical DOIs.
    :returns: A list of DOIs URLs.

    >>> to_url('1506.06690')
    'http://arxiv.org/abs/1506.06690'

    >>> to_url('1506.06690v1')
    'http://arxiv.org/abs/1506.06690v1'

def to_url(arxiv_ids):
    """
    Convert a list of canonical DOIs to a list of DOIs URLs.

    :param dois: List of canonical DOIs.
    :returns: A list of DOIs URLs.

    >>> to_url('1506.06690')
    'http://arxiv.org/abs/1506.06690'

    >>> to_url('1506.06690v1')
    'http://arxiv.org/abs/1506.06690v1'
    """
    if isinstance(arxiv_ids, list):
        return [ARXIV_URL.format(arxiv_id=arxiv_id) for arxiv_id in arxiv_ids]
    else:
        return ARXIV_URL.format(arxiv_id=arxiv_ids)