gistfile1.py

def bin_search(f, y, lo, hi, tol, nmax):
        mid = (hi + lo)/2.
        if f(lo) < y < f(hi) or f(lo) > y > f(hi):
                for i in range(nmax):
                        fmid = f(mid)
                        if abs(fmid - y) <= tol: break
                        if (fmid < y and f(lo) < f(hi)) or (fmid > y and f(lo)>f(hi)):
                                #going right
                                lo = mid
                        else:
                                #going left
                                hi = mid
                        mid = (hi+lo)/2.
                return fmid
        else:
                raise ValueError("end points don't bracket the target")