Interface analysis

When trying to call Interface I get the error:

<ipython-input-2-aa768c5df9d3> in <module>()
----> 1 from Bio.PDB import Interface

/Users/Angelica/anaconda/lib/python2.7/site-packages/Bio/PDB/Interface.py in <module>()
      8 from Bio.PDB.Entity import Entity
      9 from Bio.Data import IUPACData
---> 10 from Bio.SCOP.Raf import to_one_letter_code
     11 from Bio.PDB.PDBParser import PDBParser
     12 from Bio.PDB.NACCESS import NACCESS

ImportError: cannot import name to_one_letter_code

After some inspection of Raf.py I noticed that there is no object to_one_letter_code but one_letter_code