Saturday, 7 May 2011

pylibftdi 0.8 released; testing, coverage, and mocking

pylibftdi is a file-like wrapper to FTDI USB devices such as the UB232R (a USB<->serial converter) and the UM245R (8 bit parallel I/O).

No big changes for the 0.8 release, but a couple of new things:

  • ability to specify the device identifier in the Device([device_id]) constructor as either a serial number (as previously), or a device description. So can now specify Device('UB232R'), and the first attached UB232R device will be opened. The code initially tries to open by serial number, and if that fails will try to open by description, which I'm fairly confident will be useful rather than annoying :-)
  • more file-like API functions (flush, readline()/readlines()/writelines(), iterating over lines). These probably only make sense for text over serial lines, but that's a use-case worth supporting, considering pylibftdi already has unicode support.

As well as that, I finally got round to adding some tests, and discovered something wonderful: checking test coverage isn't just practical icing on the cake to make sure things are tested well, but is a powerful and effective motivation for writing tests. I'm using coverage, and have to say it's one of those things I wish I had got round to sooner.

Speaking of which, at some point I'll probably end up saying the same about Mock, which I've read around and know I should probably start using, but it's just so easy in Python to knock up something like this:

fn_log = []
class SimpleMock(object):
    """
    This is a simple mock plugin for fdll which logs any calls
    made through it to fn_log, which is currently rather ugly
    global state.
    """
    def __init__(self, name="<base>"):
        self.__name = name

    def __getattr__(self, key):
        # This makes me smile :)
        return self.__dict__.get(key, SimpleMock(key))

    def __call__(self, *o, **k):
        fn_log.append(self.__name)
        # most fdll calls return 0 for success
        return 0

def get_calls(fn):
    "return the called function names which the fdll mock object made"
    del fn_log[:]
    fn()
    return fn_log

Sometimes I think Python makes 'clever' things like that too easy, and is perhaps the reason that although in the Python language there is only-one-way-to-do-it, in the Python ecosystem there is perhaps a tendency to reinvent the wheel over and over again. Because it's easy - and it's fun.

As always code is at bitbucket. For the next release (0.9) I'm planning to add more tests and docs (which are rather scarce), as well as one or two of the other things I've got planned (possible D2XX support, or at least some notes on libftdi on Windows, more examples & protocol adapters, maybe even a web interface for 8 bit IO...)

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