sympy/sympy — pull request #1104 by smichr (2012-03-04 10:14:29+00:00)
Title: allow Pow, exp, log to answer is_rational if possible

http://planetmath.org/encyclopedia/TheoryOfRationalAndIrrationalNumbers.html
says the following about combinations of Rational and irrational numbers:

the sum, difference, product and quotient of two non-zero real numbers,
from which one is rational and the other irrational, is irrational.

With this change, SymPy appears to be able to follow such conventions with
the existing assumptions system and avoids answering that expressions
involving more than 1 surd are irrational.