Float approximation

approx.py

class Approx(object):
    """
    Represents an approximate floating point number. Will compare equal
    to any float-convertible type that are within 'tolerance' difference.
    
    >>> 10.0 == Approx(10.0)
    True
    >>> 10.0 == Approx(10.0001)
    False
    >>> 10.0 == Approx(10.0000000001)
    True
    >>> 10.0 == Approx(10.0001, tolerance=1e3)
    True
    
    # Forces explicit removal of approximateness
    
    >>> float(Approx(10.0))
    Traceback (most recent call last):
    RuntimeError: Approx does not permit float conversion. Use .value
    
    # Use .value property to retrieve:
    
    >>> float(Approx(10.0).value)
    10.0
    """
    def __init__(self, value, tolerance=1e-6):
        self._val = float(value)
        self._tol = tolerance
    
    def __eq__(self, other):
        return abs(self._val - float(other)) <= self._tol

    def __ne__(self, other):
      return not self == other

    def __float__(self):
        raise RuntimeError("Approx does not permit float conversion. Use .value")
    
    def __int__(self):
        raise RuntimeError("Approx does not permit integer conversion. Use .value")

    def __long__(self):
        raise RuntimeError("Approx does not permit long integer conversion. Use .value")

    def __complex__(self):
        raise RuntimeError("Approx does not permit complex conversion. Use .value")

    def __coerce__(self):
        # Do not allow coercions
        return None

    @property
    def value(self):
      return self._val

if __name__ == "__main__":
    import doctest
    doctest.testmod()