Minor: print statements in Example code fail on motor4.throttle

[larryfast]

In my test environment "motor4.throttle" fails.
examples/dc_motor.py: line 35
print("throttle:", motor4.throttle)
Looks like the getter (@properties) code isn't working as expected

Thanks for maintaining excellent demo code!

My environment:
Adafruit HUZZAH
CircuitPython version: adafruit-circuitpython-feather_huzzah-2.3.1.bin
Bundle: adafruit-circuitpython-bundle-2.3.1-mpy-20180630.zip

Bundle downloaded by ampy ... put lib

[tannewt]

How is it failing?

[dhalbert]

I traced this down:

>>> motor4.throttle
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "adafruit_motor/motor.py", line 60, in throttle
  File "adafruit_pca9685.py", line 75, in duty_cycle
  File "adafruit_register/i2c_struct_array.py", line 71, in __getitem__
TypeError: function does not take keyword arguments

The problem is actually that struct.unpack_from(format, buffer, offset=0) as implemented in shared-bindings/struct/__init__.c does not allow offset as a keyword argument, even though adafruit_register/i2c_struct_array.py calls it that way:

        return struct.unpack_from(self.format, buf, offset=1)

So this is a CircuitPython bug.

[dhalbert]

This needs to be fixed by fixing adafruit/circuitpython#984. Thanks for finding this!