Question

I’m using a Labjack for some Digital I/O with python 2.7.3 32bit and encounter the following:

This is the labjack u6 function I’m calling:

    class PortStateRead(FeedbackCommand):
    """
    PortStateRead Feedback command

    Reads the state of all digital I/O.

    >>> d.getFeedback( u6.PortStateRead() )
    [ { 'FIO' : 10, 'EIO' : 0, 'CIO' : 0 } ]
    """
    def __init__(self):
        self.cmdBytes = [ 26 ]

    def __repr__(self):
        return "<u6.PortStateRead()>"

    readLen = 3

    def handle(self, input):
        return {'FIO' : input[0], 'EIO' : input[1], 'CIO' : input[2] }

The function is returning (what appears to be) a dictionary, but when I assign the return to a variable it is assigned as a list.

    >>> import u6
    >>> handle = u6.U6()
    >>> x = handle.getFeedback(u6.PortStateRead())
    >>> x
    [{'CIO': 15, 'FIO': 255, 'EIO': 255}]
    >>> x['FIO']
    Traceback (most recent call last):
      File "<stdin>", line 1, in <module>
      TypeError: list indices must be integers, not str

Assigning x[0] to a new variable assigns as a dictionary

    >>> y = x[0]
    >>> y['FIO']
    255

Can someone explain this behavior to me please?

In the example call in the docstring the function returns a list, so I can assume this behavior is normal.

Answer 1

The function is returning (what appears to be) a dictionary…

No, it’s a dictionary in a list. The square brackets are part of the value.

>>> [{'foo':'bar'}][0]
{'foo': 'bar'}