code: def compute_nb_samples(in_prefix):
      
      file_name = in_prefix + ".tfam"
      nb = None
      with open(file_name, 'rb') as input_file:
          nb = len(input_file.readlines())
      return nb
docs: Check the number of samples.
  
      :param in_prefix: the prefix of the input file.
  
      :type in_prefix: str
  
      :returns: the number of sample in ``prefix.fam``.