Quick ln2 function for Python

ln2.py

from math import ceil

# for example, inc=4 gives ln16, or the number of hexadecimal digits
# required to represent n.
def ln2(n, inc=1):
   if n<0:
      raise ValueError('math domain error')

   i = 0
   n = int(ceil(n))
   while n:
      i += 1
      n >>= inc

   return i