code: def extract_genotypes(self, bytes):
          
          genotypes = []
          for b in bytes:
              for i in range(0, 4):
                  v = ((b>>(i*2)) & 3)
                  genotypes.append(self.geno_conversions[v])
          return genotypes[0:self.ind_count]
docs: Extracts encoded genotype data from binary formatted file.
  
          :param bytes: array of bytes pulled from the .bed file
  
          :return: standard python list containing the genotype data
  
          Only ind_count genotypes will be returned (even if there are
          a handful of extra pairs present).