title: return index of least significant bit in Python
body: <p>C++ has a set of functions, ffs(), ffsl(), and ffsll(), that return the least significant bit that is set in a given binary integer.</p>
  
  <p>I'm wondering if there is an equivalent function already available in Python. I don't see one described for bitarray, but perhaps there's another. I am hoping to avoid calculating the answer by looping through all possible bit masks, though of course that's an option of last resort; ffs() simply returns a single integer and I'd like to know of something comparable in Python.</p>