#zrbhimani(at)gmail(dot)com
def modified_base64(s):
    s_utf7 = s.encode('utf-7')
    return s_utf7[1:-1].replace('/', ',')

def modified_unbase64(s):
    s_utf7 = '+' + s.replace(',', '/') + '-'
    return s_utf7.decode('utf-7')

def encode_imap4_utf7(s, errors=None):
    """
    Encode the given C{unicode} string using the IMAP4 specific variation of
    UTF-7.

    @type s: C{unicode}
    @param s: The text to encode.

    @param errors: Policy for handling encoding errors.  Currently ignored.

    @return: C{tuple} of a C{str} giving the encoded bytes and an C{int}
        giving the number of code units consumed from the input.
    """
    r = []
    _in = []
    for c in s:
        if ord(c) in (range(0x20, 0x26) + range(0x27, 0x7f)):
            if _in:
                r.extend(['&', modified_base64(''.join(_in)), '-'])
                del _in[:]
            r.append(str(c))
        elif c == '&':
            if _in:
                r.extend(['&', modified_base64(''.join(_in)), '-'])
                del _in[:]
            r.append('&-')
        else:
            _in.append(c)
    if _in:
        r.extend(['&', modified_base64(''.join(_in)), '-'])
    return (''.join(r), len(s))