code: def strip_chr(bt):
      
      try:
          df = pd.read_table(bt.fn, header=None, dtype=str)
      # If the try fails, I assume that's because the file has a trackline. Note
      # that I don't preserve the trackline (I'm not sure how pybedtools keeps
      # track of it anyway).
      except pd.parser.CParserError:
          df = pd.read_table(bt.fn, header=None, skiprows=1, dtype=str)
      df[0] = df[0].apply(lambda x: x[3:])
      s = '\n'.join(df.astype(str).apply(lambda x: '\t'.join(x), axis=1)) + '\n'
      out = pbt.BedTool(s, from_string=True)
      return out
docs: Strip 'chr' from chromosomes for BedTool object
  
      Parameters
      ----------
      bt : pybedtools.BedTool
          BedTool to strip 'chr' from.
  
      Returns
      -------
      out : pybedtools.BedTool
          New BedTool with 'chr' stripped from chromosome names.