MCP4922 WebIOPi doesn't work, giving a type error instead

Question

I have some problem with DAC MCP4922 in my Raspberry Pi 2.

I use WebIOPi because this DAC is supported device, but when write in Configuration File (command: sudo nano /etc/webiopi/config ) line:

dac = MCP4922

in [DEVICES] section and when I try start server I see something like this:

2015-08-01 14:21:55 - WebIOPi - ERROR - __init__() takes exactly 4 arguments (3 given)
Traceback (most recent call last):
  File "/usr/local/lib/python3.2/dist-packages/WebIOPi-0.7.1-py3.2-linux-armv7l.egg/webiopi/__main__.py", line 75, in <module>
    main(sys.argv)
  File "/usr/local/lib/python3.2/dist-packages/WebIOPi-0.7.1-py3.2-linux-armv7l.egg/webiopi/__main__.py", line 69, in main
    server = Server(port=port, configfile=configfile, scriptfile=scriptfile)
  File "/usr/local/lib/python3.2/dist-packages/WebIOPi-0.7.1-py3.2-linux-armv7l.egg/webiopi/server/__init__.py", line 66, in __init__
    manager.addDevice(name, driver, args)
  File "/usr/local/lib/python3.2/dist-packages/WebIOPi-0.7.1-py3.2-linux-armv7l.egg/webiopi/devices/manager.py", line 28, in addDevice
    dev = devClass()
  File "/usr/local/lib/python3.2/dist-packages/WebIOPi-0.7.1-py3.2-linux-armv7l.egg/webiopi/devices/analog/mcp492X.py", line 52, in __init__
    MCP492X.__init__(self, chip, 2)
TypeError: __init__() takes exactly 4 arguments (3 given)

I don't have idea what to do.

Answer 1

This is a bug in the WebIOPi project.

In the mcp492X.py module, the MCP492X takes 3 arguments (over and above the default self argument):

class MCP492X(SPI, DAC):
    def __init__(self, chip, channelCount, vref):

but the 2 subclasses in that file do not pass on the vref parameter:

class MCP4921(MCP492X):
    def __init__(self, chip=0, vref=3.3):
        MCP492X.__init__(self, chip, 1)

class MCP4922(MCP492X):
    def __init__(self, chip=0, vref=3.3):
        MCP492X.__init__(self, chip, 2)

You can fix this by simply passing on the vref parameter yourself:

class MCP4921(MCP492X):
    def __init__(self, chip=0, vref=3.3):
        MCP492X.__init__(self, chip, 1, vref)

class MCP4922(MCP492X):
    def __init__(self, chip=0, vref=3.3):
        MCP492X.__init__(self, chip, 2, vref)

You can do this by editing /usr/local/lib/python3.2/dist-packages/WebIOPi-0.7.1-py3.2-linux-armv7l.egg/webiopi/devices/analog/mcp492X.py directly.

The vref argument was added to fix issue #48, but the developer only added it to the method signatures and forgot to pass on the parameter in the subclasses.

I've filed issue #159 to have the project fix this.