code: def createPopulationFile(inputFiles, labels, outputFileName):
      
      outputFile = None
      try:
          outputFile = open(outputFileName, 'w')
      except IOError:
          msg = "%(outputFileName)s: can't write file"
          raise ProgramError(msg)
  
      for i in xrange(len(inputFiles)):
          # For each file
          fileName = inputFiles[i]
          label = labels[i]
  
          try:
              with open(fileName, 'r') as inputFile:
                  for line in inputFile:
                      row = line.rstrip("\r\n").split(" ")
  
                      # Getting the informations
                      famID = row[0]
                      indID = row[1]
  
                      # Printing to file
                      print >>outputFile, "\t".join([famID, indID, label])
          except IOError:
              msg = "%(fileName)s: no such file" % locals()
              raise ProgramError(msg)
  
      # Closing the output file
      outputFile.close()
docs: Creates a population file.
  
      :param inputFiles: the list of input files.
      :param labels: the list of labels (corresponding to the input files).
      :param outputFileName: the name of the output file.
  
      :type inputFiles: list
      :type labels: list
      :type outputFileName: str
  
      The ``inputFiles`` is in reality a list of ``tfam`` files composed of
      samples. For each of those ``tfam`` files, there is a label associated with
      it (representing the name of the population).
  
      The output file consists of one row per sample, with the following three
      columns: the family ID, the individual ID and the population of each
      sample.