def decompress(compressed, uncompressed):
'''First, read a Huffman tree from the 'compressed' stream using your
read_tree function. Then use that tree to decode the rest of the
stream and write the resulting symbols to the 'uncompressed'
stream.
Args:
compressed: A file stream from which compressed input is read.
uncompressed: A writable file stream to which the uncompressed
output is written.
'''
comp = BitReader(compressed)
uncomp = BitWriter(uncompressed)
tree = read_tree(comp)
while True:
try:
uncomp_byte = huffman.decode(tree, comp)
if uncomp_byte == None:
raise EOFError
uncomp.writebits(uncomp_byte, 8)
except EOFError:
uncomp.writebits(29, 8)
break
def extract(self, output_file):
"""
Restore the compressed data
"""
br = BitReader(self.file)
root = self._read_trie(br)
# number of bytes to write
length = int(br.readbits(8))
bw = BitWriter(output_file)
# decode using the Huffman trie
for i in xrange(length):
node = root
while not node.is_leaf:
bit = br.readbit()
if bit:
node = node.right
else:
node = node.left
# write the character to output
bw.writebits(node.char, 8)
def compress(self, output_file):
"""
Compress data from input file and write compressed data to the output file.
"""
# create a ternary search trie and fill it with single ASCII characters
st = TernarySt()
for i in xrange(self.radix):
st[chr(i)] = i
code = self.radix + 1
# read all the data from the input file (not optimal, but easy to code)
data = self.file.read()
bw = BitWriter(output_file)
while len(data) > 0:
lp = st.longest_prefix(data)
# write the value of the prefix to output
bw.writebits(st[lp], self.codeword_width)
if len(lp) < len(data) and code < self.codeword_limit:
# add new prefix to the symbol table
st[data[:len(lp) + 1]] = code
code += 1
data = data[len(lp):]
bw.writebits(self.radix, self.codeword_width)
def compress(self, output_file):
"""
Compress data from input file and write compressed data to the output file.
"""
# create a ternary search trie and fill it with single ASCII characters
st = TernarySt()
for i in xrange(self.radix):
st[chr(i)] = i
code = self.radix + 1
# read all the data from the input file (not optimal, but easy to code)
data = self.file.read()
bw = BitWriter(output_file)
while len(data) > 0:
lp = st.longest_prefix(data)
# write the value of the prefix to output
bw.writebits(st[lp], self.codeword_width)
if len(lp) < len(data) and code < self.codeword_limit:
# add new prefix to the symbol table
st[data[:len(lp) + 1]] = code
code += 1
data = data[len(lp):]
bw.writebits(self.radix, self.codeword_width)
def compress(self, output_file):
"""
Compress data from input file and write compressed data to the output file.
"""
# read input and count chars
freq = defaultdict(int)
length = 0
while True:
# read one char from a file
char = self.file.read(1)
if char:
length += 1
freq[ord(char)] += 1
else:
# EOF
break
# build Huffman trie
root = self._build_trie(freq)
# build symbol table for chars and their binary representation
st = dict()
self._build_code(st, root, '')
bw = BitWriter(output_file)
# write the Huffman trie binary representation to the file
self._write_trie(root, bw)
# write number of bytes in original uncompressed message
bw.writebits(length, 8)
# use Huffman code to encode input
for i in xrange(length):
self.file.seek(i)
code = st[ord(self.file.read(1))]
for c in code:
if c == '0':
bw.writebit(False)
else:
bw.writebit(True)
