def split(s, esc='\\', sep=' '):
    """
    enhance the split func of str,
    support escape default '\' single-back-slash
    >>> split('www.abc.com\.a', sep='.')
    ['www', 'abc', 'com.a']
    """
    l = []
    ss = []
    for c in s:
        if c == esc:
            l.append(c)
        else:
            [ss.append(esc) for i in range(len(l) // 2)]
            if c == sep:
                if len(l) % 2 != 0:  # is escaped char
                    ss.append(sep)
                else:
                    ss.append(' ')

                l.clear()

            else:
                ss.append(c)

    return ''.join(ss).split(' ')