import math

class EFloat(float):
    """EFloat(x) -> floating point number with engineering representation when printed
       Convert a string or a number to a floating point number, if possible.
       When asked to render itself for printing (via str() or print) it is normalized
       to engineering style notation at powers of 10 in multiples of 3
       (for micro, milli, kilo, mega, giga, etc.)        
    """
    precision = 3
    
    def __init__(self, value=0.0):
        super(EFloat, self).__init__(value)
    
    def _exponent(self):   
        if self == 0.0:
           ret = 0
        else:
           ret = math.floor(math.log10(abs(self)))
        return ret
       
    def _mantissa(self):
        return self/math.pow(10, self._exponent())
       
    def _asEng(self):
        shift = self._exponent() % 3

        format_string = "%3." + ("%d" % EFloat.precision) + "fe%+d"
        retval = format_string % (self._mantissa()*math.pow(10, shift), self._exponent() - shift)
        return retval

    def __str__(self):
        return self._asEng()
    
    def __repr__(self):
        return str(self)

    def __add__(self, x):
        return EFloat(float.__add__(self, float(x)))

    def __radd__(self, x):
        return EFloat(float.__add__(self, float(x)))
 
    def __mul__(self, x):
        return EFloat(float.__mul__(self, float(x)))

    def __rmul__(self, x):
        return EFloat(float.__mul__(self, float(x)))

    def __sub__(self, x):
        return EFloat(float.__sub__(self, float(x)))

    def __rsub__(self, x):
        return EFloat(float.__rsub__(self, float(x)))

    def __div__(self, x):
        return EFloat(float.__div__(self, float(x)))

    def __rdiv__(self, x):
        return EFloat(float.__rdiv__(self, float(x)))

    def __truediv__(self, x):
        return EFloat(float.__truediv__(self, float(x)))

    def __rtruediv__(self, x):
        return EFloat(float.__rtruediv__(self, float(x)))

    def __pow__(self, x):
        return EFloat(float.__pow__(self, float(x)))

    def __rpow__(self, x):
        return EFloat(float.__rpow__(self, float(x)))

    def __divmod__(self, x):
        return EFloat(float.__divmod__(self, float(x)))

    def __neg__(self):
        return EFloat(float.__neg__(self))

    def __floordiv__(self, x):
        return EFloat(float.__floordiv__(self, float(x)))