How to count the Index of an instance?

Question

I want to start multiple servers like this:

Server 1
Server 2
Server 3

I have already written a code:

class Server:
     def __init__(self, index):
          self.index = index

My main is looking like this:

server1 = Server(1)
server1.run()

So my question is as you can read in the captio: How can I global count the Index of different instances (Servers) dynamically?

Answer 1

Store the total instance count in a class variable.

class Server:
    instances = 0   
    def __init__(self):
         Server.instances += 1
         self.index = Server.instances

Solving this problem across multiple instances requires more work. You must use a file to hold the counter, and you must ensure that two processes don't fight over who gets to open the file next. This should work on Linux:

import fcntl
class Server:
    CNTR = 'mycounter.txt'
    def __init__(self):
        if not os.path.exists(CNTR):
            open(CNTR,'w').write('0')
        fctl.lock( f, fcntl.LOCK_EX )
        n = int(open(CNTR).read()) + 1
        open(CNTR,'w').write(str(n))
        fctl.lock( f, fcntl.LOCK_UN )

        self.index = n