Hallöchen! Peter Hansen <[EMAIL PROTECTED]> writes:
> Torsten Bronger wrote: > >> Peter Hansen <[EMAIL PROTECTED]> writes: >> >>> What's your use case for del? >> >> Every instance represents a "session" to a measurement instrument. >> After the instance is deleted, the session should be closed to free >> resources. > > You mean like GPIB devices? Yes. > We've written a lot of software that talks to instruments, as well > as pumps, motors, and sensors of all kinds. I haven't even needed > to "free resources", other than by closing a serial port, for > example. [...] I've just finished a thin-wrappers implementation of VISA in Python, see <http://pyvisa.sf.net/>. It calls functions in a proprietary VISA DLL/SO. The next step is to build a simple-to-use OO layer on top of it. Therefore, we don't communicate with the device directly, but via sessions (=handles) within the DLL. These sessions should be freed when the object instance representing the device is destroyed by Python. Using the __del__ method is the natural choice for this in my opinion. > [...] I'd recommend pretending __del__ does not exist and > restructuring your system to close these sessions explicitly, > under your direct control, at the appropriate point. This has > worked very well for us so far. I'd find this quite sad because so far it's drop-dead simple to use the OO layer, and I may even convince our in-house HT Basic fans of Python: keithley = GpibInstrument(14) keithley.write("*IDN?") print keithley.read() A keithley.close() would be a wart in my opinion; instead I want to hide the whole session thing from the programmer. Besides, I haven't yet given up the hope that the issues with __del__ can be tackled. Tschö, Torsten. -- Torsten Bronger, aquisgrana, europa vetus -- http://mail.python.org/mailman/listinfo/python-list
