'Return the units for column in axis'

def columnUnits(self, axis, column):

    ax = self._info[self._interpretAxis(axis)]
    if ('cols' in ax):
        for c in ax['cols']:
            if (c['name'] == column):
                return c['units']
        raise Exception(('Axis    %s    has    no    column    named    %s' % (str(axis), str(column))))
    else:
        raise Exception(('Axis    %s    has    no    column    definitions' % str(axis)))
