'Return our interface object with given string name,
default intf if name is falsy (None, empty string, etc).
or the input intf arg.
Having this fcn return its arg for Intf objects makes it
easier to construct functions with flexible input args for
interfaces (those that accept both string names and Intf objects).'

def intf(self, intf=None):

    if (not intf):
        return self.defaultIntf()
    elif isinstance(intf, basestring):
        return self.nameToIntf[intf]
    else:
        return intf
