code: def _boundsspec2slicespec(boundsspec,scs):
          
          l,b,r,t = boundsspec
  
          t_m,l_m = scs.sheet2matrix(l,t)
          b_m,r_m = scs.sheet2matrix(r,b)
  
          l_idx = int(np.ceil(l_m-0.5))
          t_idx = int(np.ceil(t_m-0.5))
          # CBENHANCEMENT: Python 2.6's math.trunc()?
          r_idx = int(np.floor(r_m+0.5))
          b_idx = int(np.floor(b_m+0.5))
  
          return t_idx,b_idx,l_idx,r_idx
docs: Convert an iterable boundsspec (supplying l,b,r,t of a
          BoundingRegion) into a Slice specification.
  
          Includes all units whose centers are within the specified
          sheet-coordinate bounds specified by boundsspec.
  
          Exact inverse of _slicespec2boundsspec().