like_units(a,b) yields True if a and b can be cast to each other in terms of units and False
      otherwise. Non-united units are considered dimensionless units.

def like_units(a, b):
    '''
    like_units(a,b) yields True if a and b can be cast to each other in terms of units and False
      otherwise. Non-united units are considered dimensionless units.
    '''
    a = quant(0.0, a) if is_unit(a) else a if is_quantity(a) else quant(a, units.dimensionless)
    b = quant(0.0, b) if is_unit(b) else b if is_quantity(b) else quant(b, units.dimensionless)
    if a == b: return True
    try:
        c = a.to(b.u)
        return True
    except:
        return False