Python Forum

Hi Everybody,

I have some experience in programming pascal / delphi and C++.
So this means I know the basic concepts. But I have almost no knoweldge about python its functions and the syntax.

I would like to have some advice for the basic concept.
I want to write code with this functionality:

Computer A sends a heartbeat signal over network once every minute towards a computer B.

Computer B is waiting to receive this heartbeat-signalfrom Computer A.
Whenever the heartbeat-signal is received nothing else shall happen.
If no heartbeat-signal is received by computer B within one minute
the python-code running on computer B shall start to count up
count = 1
2 minutes no heartbeat-signal count = 2
3 minutes no heartbeat-signal count = 3
4 minutes no heartbeat-signal count = 4
5 minutes no heartbeat-signal count = 5

if variable count has reached value 5 computer B shall execute code that sends an email.
This email shall only be sent a single time.
After sending the email one single time computer B shall just wait for heartbeat-signals and do nothing else
If a new heartbeat-signal is received by computer B
The code running on computer B shall start checking for following up heartbeat-signals the same way as described above
If computer B does not receive new heartbeat-signals
the python-code running on computer B shall start to count up
count = 1
2 minutes no heartbeat-signal count = 2
3 minutes no heartbeat-signal count = 3
4 minutes no heartbeat-signal count = 4
5 minutes no heartbeat-signal count = 5

and this cycle repeats.

As I am very new to python I don't know what basic concept to choose to obtain this functionality with rather simple code than
high sophisticated code that is hard to understand

basic ideas that I have:
send a short UDP-message from computer A to computer B
acting on th ereceived UDP-message.

I have made some initial steps by send and receive UDP-messages but with the receiver-code that I have found online
the code is blocked inside the line

data,addr = sock.recvfrom(1024)        #receive data from client

So I can't check if the heartbeat-signal received within a minute
I made a try to use a child-thread but have problems to use variables between the threads

I tried saving the UDP-message into a textfile
and have another code looking onto the harddisk if this file is present which lead to access-denied errors

So this is why I am asking here what basic concept to use
will it be easier to use global variables in threads
or does this not work at all and I should use this "queing mechanism ?

would it be easier to use some kind of try -except construction ?
You may find try - except "ugly" coding.
As this is only about a heartbeat-signal a few bytes once per minute I don't care about the computational power this needs

What do you suggest as the basic concept?
If you could mention at least some keywords so I can lookup these keywords for code-examples this would be sufficient.
Any code-examples that go into the right direction are welcomed of course

best regards Stefan

You could start a thread that reads from the socket and fills a queue.Queue

input_queue = queue.Queue()

class ReaderThread(Thread):
    def run(self):
        ... # create socket
        while True:
            item = sock.recvfrom(1024)
            input_queue.put(item)

Then you start the thread and you read from the queue with a timeout

reader = ReaderThread()
reader.start()
while True:
    for no_heartbeat_count in range(5):
        try:
            data, addr = input_queue.get(timeout=60)
        except queue.Empty:
            pass
        else:
            input_queue.task_done()
            break
    else:
        send_email()
        continue
    process_item(data, addr)