how does python calculate square roots?

Question

I noticed that square roots are pretty fast in python.

import time
a = time.time()
print((1234567891011121314151617181920**8)**0.5)
d = time.time()-a
print(d)

output:

2.32305723559e+120
0.0150001049042

That's a 200+ digit number in under 0.1 second!

So what's the algorithm behind all this?

Answer 1

CPython is just calling the C intrinsic pow in this case, letting the compiler do whatever it wants with it. How to: pow(real, real) in x86 is one example of somewhere explaining a fast implementation of pow at a processor level.