Calculating the length of the hypotenuse using the standard formula c = sqrt(a**2 + b**2) may lead to overflow if the two other sides are both very large. Even though c will not be much bigger than max(a, b), either a**2 or b**2 (or both) will. Thus, the calculation could overflow, even though the result is well within representable range.

Rather than sqrt(a**2 + b**2), use the built-in function hypot(a,b) from the math library.

The following code shows two different ways of computing the hypotenuse. The first is a direct rewrite of the Pythagorean theorem, the second uses the built-in function.

Python Language Reference: The hypot function

Wikipedia: Hypot.