old_contents: """
      Longest Common Sunsequence
      --------------------------
      Implements the dynamic programming solution to the longest common
      subsequence algorithm.
  
      Pseudo Code:
      http://en.wikipedia.org/wiki/Longest_common_subsequence_problem
  """
  
  
  def build_lengths_matrix(str1, str2):
      """
      XXX: Needs documentation written.
      """
      matrix = [[0 for j in range(len(str2)+1)] for i in range(len(str1)+1)]
      for i, x in enumerate(str1):
          for j, y in enumerate(str2):
              if x == y:
                  matrix[i+1][j+1] = matrix[i][j] + 1
              else:
                  matrix[i+1][j+1] = max(matrix[i+1][j], matrix[i][j+1])
      return matrix
  
  
  def read_from_matrix(matrix, str1, str2):
      """
      XXX: Needs documentation written.
      """
      result = ""
      i, j = len(str1), len(str2)
      while i != 0 and j != 0:
          if matrix[i][j] == matrix[i-1][j]:
              i -= 1
          elif matrix[i][j] == matrix[i][j-1]:
              j -= 1
          else:
              result += str1[i-1]
              i -= 1
              j -= 1
      return result[::-1]
  
  
  def lcs(str1, str2):
      """
      XXX: Needs documentation written.
      """
      lengths = build_lengths_matrix(str1, str2)
      return read_from_matrix(lengths, str1, str2)
  
new_contents: """
      Longest Common Subsequence
      --------------------------
      Implements the dynamic programming solution to the longest common
      subsequence algorithm.
  
      Pseudo Code:
      http://en.wikipedia.org/wiki/Longest_common_subsequence_problem
  """
  
  
  def build_lengths_matrix(str1, str2):
      """
      XXX: Needs documentation written.
      """
      matrix = [[0 for j in range(len(str2)+1)] for i in range(len(str1)+1)]
      for i, x in enumerate(str1):
          for j, y in enumerate(str2):
              if x == y:
                  matrix[i+1][j+1] = matrix[i][j] + 1
              else:
                  matrix[i+1][j+1] = max(matrix[i+1][j], matrix[i][j+1])
      return matrix
  
  
  def read_from_matrix(matrix, str1, str2):
      """
      XXX: Needs documentation written.
      """
      result = ""
      i, j = len(str1), len(str2)
      while i != 0 and j != 0:
          if matrix[i][j] == matrix[i-1][j]:
              i -= 1
          elif matrix[i][j] == matrix[i][j-1]:
              j -= 1
          else:
              result += str1[i-1]
              i -= 1
              j -= 1
      return result[::-1]
  
  
  def lcs(str1, str2):
      """
      XXX: Needs documentation written.
      """
      lengths = build_lengths_matrix(str1, str2)
      return read_from_matrix(lengths, str1, str2)
  
subject: Update lcs.py