def _expandCipherString(cipherString, method, options):
    """
    Expand C{cipherString} according to C{method} and C{options} to a list
    of explicit ciphers that are supported by the current platform.

    @param cipherString: An OpenSSL cipher string to expand.
    @type cipherString: L{unicode}

    @param method: An OpenSSL method like C{SSL.TLSv1_METHOD} used for
        determining the effective ciphers.

    @param options: OpenSSL options like C{SSL.OP_NO_SSLv3} ORed together.
    @type options: L{int}

    @return: The effective list of explicit ciphers that results from the
        arguments on the current platform.
    @rtype: L{list} of L{ICipher}
    """
    ctx = SSL.Context(method)
    ctx.set_options(options)
    try:
        ctx.set_cipher_list(cipherString.encode('ascii'))
    except SSL.Error as e:
        # OpenSSL 1.1.1 turns an invalid cipher list into TLS 1.3
        # ciphers, so pyOpenSSL >= 19.0.0 raises an artificial Error
        # that lacks a corresponding OpenSSL error if the cipher list
        # consists only of these after a call to set_cipher_list.
        if not e.args[0]:
            return []
        if e.args[0][0][2] == 'no cipher match':
            return []
        else:
            raise
    conn = SSL.Connection(ctx, None)
    ciphers = conn.get_cipher_list()
    if isinstance(ciphers[0], unicode):
        return [OpenSSLCipher(cipher) for cipher in ciphers]
    else:
        return [OpenSSLCipher(cipher.decode('ascii')) for cipher in ciphers]

    Expand C{cipherString} according to C{method} and C{options} to a list
    of explicit ciphers that are supported by the current platform.

    @param cipherString: An OpenSSL cipher string to expand.
    @type cipherString: L{unicode}

    @param method: An OpenSSL method like C{SSL.TLSv1_METHOD} used for
        determining the effective ciphers.

    @param options: OpenSSL options like C{SSL.OP_NO_SSLv3} ORed together.
    @type options: L{int}

    @return: The effective list of explicit ciphers that results from the
        arguments on the current platform.
    @rtype: L{list} of L{ICipher}
    
stackoverflow/venv/lib/python3.6/site-packages/twisted/internet/_sslverify.py