Implementing use of ‘with object() as f’ in custom class in python

Those methods are pretty much all you need for making the object work with with statement.

In __enter__ you have to return the file object after opening it and setting it up.

In __exit__ you have to close the file object. The code for writing to it will be in the with statement body.

class Meter():
    def __init__(self, dev):
        self.dev = dev
    def __enter__(self):
        #ttysetattr etc goes here before opening and returning the file object
        self.fd = open(self.dev, MODE)
        return self
    def __exit__(self, type, value, traceback):
        #Exception handling here
        close(self.fd)

meter = Meter('dev/tty0')
with meter as m:
    #here you work with the file object.
    m.fd.read()