Python Programming On Win32

The Microsoft Communications Control (MSComm)

Microsoft has provided a COM interface to the serial port in the form of an OCX. This gives less detailed control than the Python Serial package, but is adequate for the kind of examples above. It’s distributed with Visual Basic, Visual Studio, and most Microsoft development tools; you need one of these packages to redistribute it. In a corporate setting this isn’t usually a problem. Unlike the Serial package, it requires the Python COM framework. Let’s talk to a modem with it, this time reverting to a plain old system connected with real wires:

def MSCommDemo():
    #talks to a modem on COM1
    from win32com.client import Dispatch
    comm = Dispatch('MSCOMMLib.MSComm')
    comm.CommPort = 1    #COM1
    comm.PortOpen = 1
    try:
        comm.Output = "AT\015"               # add a carriage return
        inbuf = ''
        now = time.time()
        elapsed = time.time() - now
        while (string.find(inbuf, 'OK') < 0) and (elapsed < 2):
            inbuf = inbuf + str(comm.Input)  #remember the Unicode string!
            elapsed = time.time() - now
        print inbuf
    finally:
        comm.PortOpen = 0

When run, you should see your command of AT echoed, followed by the response OK. Note that you don’t know how long it will take to respond, so you loop until you get the desired data or until some time limit has elapsed. This behavior was wrapped for us by Serial.py, and you could wrap it here as well if you were going to use the MSComm control a lot.

One truly amazing thing about the MSComm control is the syntax. Microsoft loves properties; we saw ...