Python values with units

Question

I need to keep track of units on float and int values in Python, but I don't want to use an external package like magnitude or others, because I don't need to perform operations on the values. Instead, all I want is to be able to define floats and ints that have a unit attribute (and I don't want to add a new dependency for something this simple). I tried doing:

class floatwithunit(float):

    __oldinit__ = float.__init__

    def __init__(self, *args, **kwargs):
        if 'unit' in kwargs:
            self.unit = kwargs.pop('unit')
        self.__oldinit__(*args, **kwargs)

But this doesn't work at all:

In [37]: a = floatwithunit(1.,unit=1.)
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)

/Users/tom/<ipython console> in <module>()

TypeError: float() takes at most 1 argument (2 given)

Any suggestions?

Answer 1

You might be looking for something like this:

class UnitFloat(float):

    def __new__(self, value, unit=None):
       return float.__new__(self, value)

    def __init__(self, value, unit=None):
        self.unit = unit


x = UnitFloat(35.5, "cm")
y = UnitFloat(42.5)

print x
print x.unit

print y
print y.unit

print x + y

Yields:

35.5
cm
42.5
None
78.0