code: def amino_acid_distribution(peptides, smoothing=0.0):
      
      peptides = pandas.Series(peptides)
      aa_counts = pandas.Series(peptides.map(collections.Counter).sum())
      normalized = aa_counts / aa_counts.sum()
      if smoothing:
          normalized += smoothing
          normalized /= normalized.sum()
      return normalized
docs: Compute the fraction of each amino acid across a collection of peptides.
      
      Parameters
      ----------
      peptides : list of string
      smoothing : float, optional
          Small number (e.g. 0.01) to add to all amino acid fractions. The higher
          the number the more uniform the distribution.
  
      Returns
      -------
      pandas.Series indexed by amino acids