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After exercising the fractions module, I've found it problematic that 
there isn't a unified constructor to handle mixed data input types. 
For example, when updating the accurate summation recipe at 
http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/393090 to show 
how it could be done with rational arithmetic. Handling mixed-type 
inputs required writing a factory function:
 def makefrac(x):
 if isinstance(x, Decimal):
 return Fraction.from_decimal(x)
 if isinstance(x, float):
 return Fraction.from_float(x)
 return Fraction(x)
That function supported a clean version of the recipe:
 def frsum(iterable):
 return float(sum(map(makefrac, iterable)))
It would have been much better if that functionality were built into 
the class definition. See attached patch.

Adopted the solution used by functions in the math module. Functions 
that accept floats also accept integral inputs. This improves 
usability in face of mixed float/int data or decimal/int data.
See r64846.