def snp_url(snpid):
    """Create url SNP ID."""
    if snpid.startswith('rs'):
        url = 'http://www.ncbi.nlm.nih.gov/snp/?term={}'.format(snpid)
        pass
    elif snpid.startswith('COSM'):
        url = (
            'http://cancer.sanger.ac.uk/cosmic/mutation/overview?genome=37\\&id={}'
            .format(snpid.lstrip('COSM')))
    elif snpid.startswith('COSN'):
        url = (
            'http://cancer.sanger.ac.uk/cosmic/ncv/overview?genome=37\\&id={}'
            .format(snpid.lstrip('COSN')))
    else:
        return snpid
    return url
