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PS. I can shave off nearly 4 usec of the constructor like this:
- self = super(Fraction, cls).__new__(cls)
+ if cls is Fraction:
+ self = object.__new__(cls)
+ else:
+ self = super().__new__(cls)
This would seem to give an upper bound for the gain you can make by
moving the check for instantiating an abstract class to C. Your call. 
I also found that F(2,3)+F(5,7) takes about 22 usecs (or 18 using the
above hack).
Inlining the common case for addition (Fraction+Fraction) made that go
down to 14 usec (combined with the above hack):
- __add__, __radd__ = _operator_fallbacks(_add, operator.add)
+ __xadd__, __radd__ = _operator_fallbacks(_add, operator.add)
 
+ def __add__(self, other):
+ if type(other) is Fraction:
+ na = self._numerator
+ da = self._denominator
+ nb = other._numerator
+ db = other._denominator
+ return Fraction(na*db + nb*da, da*db)
+ return self.__xadd__(other)
+