code: def calculate_tetra(infiles):
      
      logger.info("Running TETRA.")
      # First, find Z-scores
      logger.info("Calculating TETRA Z-scores for each sequence.")
      tetra_zscores = {}
      for filename in infiles:
          logger.info("Calculating TETRA Z-scores for %s", filename)
          org = os.path.splitext(os.path.split(filename)[-1])[0]
          tetra_zscores[org] = tetra.calculate_tetra_zscore(filename)
      # Then calculate Pearson correlation between Z-scores for each sequence
      logger.info("Calculating TETRA correlation scores.")
      tetra_correlations = tetra.calculate_correlations(tetra_zscores)
      return tetra_correlations
docs: Calculate TETRA for files in input directory.
  
      - infiles - paths to each input file
      - org_lengths - dictionary of input sequence lengths, keyed by sequence
  
      Calculates TETRA correlation scores, as described in:
  
      Richter M, Rossello-Mora R (2009) Shifting the genomic gold standard for
      the prokaryotic species definition. Proc Natl Acad Sci USA 106:
      19126-19131. doi:10.1073/pnas.0906412106.
  
      and
  
      Teeling et al. (2004) Application of tetranucleotide frequencies for the
      assignment of genomic fragments. Env. Microbiol. 6(9): 938-947.
      doi:10.1111/j.1462-2920.2004.00624.x