import sys

# Parse the command line.
if (len(sys.argv) != 2):
  print "USAGE: do-tryptic-digest.py <proteins>"
  sys.exit(1)

# Initialize the list of peptides.
myPeptides = {}

# Open the file and read it line by line.
myFile = open(sys.argv[1], "r")
for protein in myFile:
  protein = protein.rstrip()

  # Traverse the protein.
  peptideStart = 0
  for proteinIndex in range(0, len(protein)):

    # The final peptide is always tryptic.
    if (proteinIndex == len(protein) - 1):
      myPeptide = protein[peptideStart:proteinIndex + 1]
      myPeptides[myPeptide] = 1

    else:
      thisAmino = protein[proteinIndex]
      nextAmino = protein[proteinIndex + 1]

      # Check for a tryptic cleavage location.
      if (((thisAmino == "K") or (thisAmino == "R")) and
          (nextAmino != "P")):
        myPeptide = protein[peptideStart:proteinIndex + 1]
        myPeptides[myPeptide] = 1
        peptideStart = proteinIndex + 1

myFile.close()

# Print all the peptides.
for peptide in myPeptides.keys():
  print peptide