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Sorry for reopening this, but I found one more thing. Division is pretty heavy on PyLong objects and there doesn't seem to be an internal optimisation for division by 1 and -1. Since many Fraction input values can already be normalised for some reason, the following change shaves off almost 30% of the calls to PyNumber_InPlaceFloorDivide() in the telco benchmark during Fraction instantiation according to callgrind, thus saving 20% of the CPU instructions that go into tp_new().
Instead of always executing
 numerator //= g
 denominator //= g
this avoids unnecessary divisions:
 if g is not 1:
 if g is -1:
 numerator = -numerator
 denominator = -denominator
 else:
 numerator //= g
 denominator //= g
Using the "is" operator here is CPythonish, but doing the same with != and == should also be an improvement already, although not as cheap. Now, given that CPython caches small integers internally, I would suggest actually not adding these two special cases to the fractions module but more generally to the division routines in longobject.c.