How to locally redefine __truediv__ to return Fraction

Question

In Python 3, division of integers, or anything including a float, results in a float:

>>> from fractions import Fraction
>>> f = Fraction(1, 2)
>>> f / 2
Fraction(1, 4)
>>> 2 / f
Fraction(4, 1)
>>> 1 / 2 
0.5
>>> 2 / 1 
2.0
>>> f / .1
5.0
>>> f / .2
2.5
>>> .2 / f
0.4

I would like to get division to return Fractions, i.e., get the following behavior:

>>> 1 / 2
Fraction(1, 2)
>>> 2 / 1
Fraction(2, 1)

I have unsuccessfully tried to redefine division:

>>> int.__truediv__ = lambda self, other: Fraction(self) / Fraction(other)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: can't set attributes of built-in/extension type 'int'

What are my options? I'm ok with introducing a MyFraction class derived from Fraction. At the least I would want to be able to define a dict-like class X such that

>>> X({'a': 1/3}) == X({'a': Fraction(1, 3)})
True

N.B.: It seems that originally, the behavior I describe was the intended one (cf. PEP 238):

If and when a rational type is added to Python (see PEP 239), true division for ints and longs should probably return a rational. This avoids the problem with true division of ints and longs losing information. But until then, for consistency, float is the only choice for true division.

Answer 1

You probably shouldn't do this, but you can monkey-patch built-in types using the Forbidden Fruit module.