Algorithms For Dummies

  Compressing Data 

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        else:

            print ('Not found:',current,'Output:',

                   reverse_dictionary[previous

                    ] 

+ reverse_dictionary[previous][0])

            s = reverse_dictionary[previous

                    ] 

+ reverse_dictionary[previous][0]

            print ('New dictionary entry %s at index %s' %

                   (s, max(reverse_dictionary.keys())

+1))

            reverse_dictionary[

                max(reverse_dictionary.keys())

+1] = s

            print ('Decompressed %s' % s)

            output 

+= s

            print ('>%s' % output)

    return output

Running the function on the previously compressed sequence recovers the origi-

nal information by scanning through the symbolic table, as shown here:

print ('\ndecompressed string : %s' %

       lzw_decompress(compressed))

print ('original string was : %s' % text)

Decompressed A

> A

Decompressed B

> AB

New dictionary entry AB at index 256

Decompressed AB

> ABAB

New dictionary entry BA at index 257

Decompressed C

> ABABC

New dictionary entry ABC at index 258

Decompressed ABC

> ABABCABC

New dictionary entry CA at index 259

Decompressed ABC

> ABABCABCABC

New dictionary entry ABCA at index 260

decompressed string : ABABCABCABC

original string was : ABABCABCABC

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