why not use logs? in python:

  >>> from math import log
  >>> def isPower2(val): return False if (val == 0) else  (log(val) / log(2)).is_integer()
  ... 
  >>> isPower2(0)
  False
  >>> isPower2(1)
  True
  >>> isPower2(2)
  True
  >>> isPower2(3)
  False
  >>> isPower2(4)
  True
  >>> isPower2(1024)
  True
  >>> isPower2(1025)
  False