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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def main(ctx, host, port, transport_type, timeout, ca_certs):
 """Connects to a Riemann server to send events or query the index By default, will attempt to contact Riemann on localhost:5555 over TCP. The RIEMANN_HOST and RIEMANN_PORT environment variables can be used to configure the host and port used. Command line parameters will override the environment variables. Use `-T none` to test commands without actually connecting to a server. """

    if transport_type == 'udp':
        if timeout is not None:
            ctx.fail('--timeout cannot be used with the UDP transport')
        transport = riemann_client.transport.UDPTransport(host, port)
    elif transport_type == 'tcp':
        transport = riemann_client.transport.TCPTransport(host, port, timeout)
    elif transport_type == 'tls':
        if ca_certs is None:
            ctx.fail('--ca-certs must be set when using the TLS transport')
        transport = riemann_client.transport.TLSTransport(
            host, port, timeout, ca_certs)
    elif transport_type == 'none':
        transport = riemann_client.transport.BlankTransport()

    ctx.obj = transport