How to work with delay between serial writing and reading

Question

My python script is working with a modem, and the first step of the process is to check if there is enough signal. Through AT commands,I can ask the modem for the signal intensity, so I made a loop that constantly asks for the strenght of the signal, and then proceeds if the signal is strong enough.

If there is signal available, it works just fine. The problem is when there is no signal. I've tried increasing the sleep time, but it seems not to work.

Signal = False

    while Signal is not True:    
        x = ser.readline()
        y = x.rstrip()
        z = y.decode('utf-8')
        ser.write(str.encode('AT+CSQ?\r'))
        time.sleep(9)
        if (z.startswith("+CSQ")):
            a = int(z[5])
            if a >= 3:
                Signal = True
                time.sleep(4)
                enough_signal_write()
            else:
                checking_signal

With long loops, like 10 tries to catch signal, it seems to work strangely, like ignoring if the signal is strong enough sometimes, then finally catching up and running. (I can check this through the strange order of the modem outputs with 'print(z)' line)

I'm feeling like I need something to wait for the modem to respond, and then take actions with this, but I'm not sure how I should do it.

Thanks for you time

You only read serial once, `x = ser.readline()`. You should be looping on that after you write. See: [Python Serial: How to use the read...](https://stackoverflow.com/a/16078029/8150685) — Error - Syntactical Remorse, Apr 16 '19 at 14:04
does it work even if my modem output is more than 1 line? the 'AT+CSQ?' command gives me more than one line as response, as an example. — vaughan is god, Apr 16 '19 at 14:10
Yes. You you have to loop till you get no more data. Read the example that I linked. You will see they loop till they can't read anymore. — Error - Syntactical Remorse, Apr 16 '19 at 14:12

How to work with delay between serial writing and reading

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