Am I an idiot or what! There were a few stupid errors in that diffing algorithm I threw up (give me a break: they don’t have python installed here in college). Here’s a corrected version. Again, any comments are welcome.

def GetDiff(oldLines, newLines): """Constructs a diff to get from newlines to oldlines.""" # Construct our special "hash" table. Using primes for the table length # would be better, I know, but odd numbers are simpler. tblSize = len(newLines) * 2 + 1 tbl = tuple([] * tblSize) for iNew in range(len(newLines)): iBucket = hash(newLines[iNew]) % tblSize tbl[iBucket].append(iNew) # Holds our diff information. result = [] # Find the common subsequences and differences. iOld = 0 iMax = 0 while iOld < len(oldLines): iBucket = hash(oldLines[iOld]) % tblSize # Start with no match nMax = 0 for iNew in tbl[iBucket]: # if nMax > 0 and iNew < iMax + nMax: # continue nCur = 0 try: while newLines[iNew + nCur] == oldLines[iOld + nCur]: nCur += 1 if nCur > nMax: nMax = nCur iMax = iNew iEnd = iMax + nMax if iEnd == len(oldLines) or iEnd == len(newLines): break # Have we found a matching subsequence? if nMax == 0: # Nope. result.append(oldLines[iOld]) iOld += 1 else: # Woohoo! result.append((iMax, nMax)) iOld += nMax return result

There old version is in my last entry.